here I'll help you out with my own mindset. Edmonton is a working class city. Most people develop an interest in career and prepare for that for years.
Particular to sports anybody that endeavors to have that as a career, and particularly in hockey, they train and play and do everything possible to be the best at that and often starting even preschool. Those that want to go pro, I've never heard athletes in present day say they never trained, never took it seriously, and couldn't even go up one flight of stairs without that being challenging.
The trouble with this is the years of his life (vast majority) where Skinner didn't train and prep in every bit of flexibility, strength, conditioning that are assets to pro goalies you can't just make that all up in the now. Supreme flexibility is had through mostly lifetime endeavor. Conditioning takes years.
Watch Skinner's poor butterfly form. (he's poor at stretching pads across relative to other NHL goalies and for his size, and thats just one aspect where not working on that for years has left him this terrible flexibility. Its just one example.
Thats the thing though. For his craft at this age he can only work on certain things. Some things are always going to be a problem, and deficiency because he didn't work on those lifelong as you have to to have supreme flexibility which is a major goalie requisite.
As far as training and prep right now I've been specific. Skinner has the laziest warmups and pregame of any goalie I've seen, ever, with the NHL Oilers. Its like he pretends at pregame edgework, flexes, skating etc. Very clear he half asses it and very clear as well when he tries to do lateral edgework with some force he often loses balance. This more than indicative he doesn't have it down. he doesn't do it enough to be consistent in movement. He has even fundamental skating difficulty. This features even in games where he's slow lumbering out or back in cage.
Another thing to watch for is how quickly proficient goalies can get up out of the Butterfly, and how many times without looking fatigued or cheating up or down. Skinner will often just stay down, or up, even as the situation in front of him requires one or the other. For instance Vasi or Quick may be up and down 5X times as much as situation merits because they have the athleticism to do that. They also feature micro up/down or one leg up or down that Skinner doesn't even have as a skillset. Skinner stays up or down with more latency because he can't spring up efficiently from butterfly. Again this is something that takes years of training.
Theres no excuse for stuff like that. Especially with the best training availability that NHL goalies have.
You can feel free to disagree with every point I've raised here but its the closest I'm prepared to go right now in speaking of the limitations
There is a lot of Strawman and a good deal of traditional Replacement bias in the above. I feel like there are probably a half-dozen of your posts on various players you decided to pick on (including several on RNH, who you now seem to finally appreciate... perhaps only because he took a discount) that start with: "This is a working class town and player so and so is lazy... don't ask me to dig up a link, you can see it in their demeanor"
To rebut a few of your actual in-good-faith points:
1) No, a modern 6'5 NHL goalie DOES NOT need to be particularly flexible. They are already big, they need a super strong core, super strong glutes and hips. That often comes at the expense of flexibility so you prioritize the former.
2) Jonathan Quick is probably the WORST comparable to Skinner in this modern era. I know you did it to contrast, but they are like an ENTIRELY DIFFERENT CLASS of goaltender. What 5'11 (if that) Quick needs to do to be successful at the NHL level and what Skinner needs to do, are entirely different. Quick does need to get up and down into butterfly twice as fast because he's going to need to do it twice as often... he can't see otherwise.
3) To the above, much of what you want out of Skinner is stylistic. You prefer J Quick's style of goaltending. Me too, I'm a huge FAN of small goalies who (absolutely have no choice but to) play with that level of agility. I am not a FAN of Skinner's style, but I do ADMIRE it. The record shows that HUGE, reasonably skating goalies are THE phenotype that is successful in the NHL. I wish this style would die off, but there is no question that it works and it's very clear that smaller, more athletic goalies have difficulty rising the ranks.
4) I do agree that skating and edge work is critical for NHL goaltending... I don't agree that Skinner is particularly a bad skater... at least I haven't noticed it at all. I will bookmark this point and have a more critical eye... but my eye test is perhaps biased by the fact that, unlike Smith and Koskinen before him, Skinner actually DOES play at the top of the crease and cut angles moreso than many HUGE goalies. To me that implies that he has the skating to patrol the full scope of the crease, whereas other big guys tend to stay deep since i) they can and ii) it reduces the lateral distance one needs to cover. I hate it... cut the damn angle like a smaller goalie would and you'd be unbeatable down-low and anywhere except top corners. Skinner generally gets this... he's not perfect, but he's much better than most.
5) What's "micro up/down". Are you talking about "V-H" = post leg up and far-side leg down or "Reverse V-H" (opposite of VH)?? Skinner doesn't do any V-H (it's very out of fashion) and does a tonne of RVH... actually (like many NHL goalies) he over-relies on it. That's why he gets sniped up by his earlobes on the short side. I hate it... but he definitely relies heavily on it, so not sure what you mean.
6) Maybe you mean butterfly pushes (some people call it pro-fly)? Like when you are down in butterfly, but raise one knee slightly to edge yourself and slide from one slide to another? To your skating point above, Skinner doesn't do a lot of pro-fly, but he's so big the distance from one post to the other when in RVH isn't much, so those pushes are much less obvious than for a smaller guy. I do think he could probably benefit from adding more of that to his bag of tricks for recovery pushes when he's out on top of the blue paint.
I stated on Skinner very early on that he doesn’t have great flexibility or athleticism, calling out his inability to do the splits.
I still don't get this. When does a modern goalie actually need to to the splits? Even on a 2-1 cross ice pass, I'd much rather have my goalie sell out fully with a full-stretched leading leg and a foundational knee on the trailing leg (like a classic "half butterfly") so that they can have their upper body and gloves in the play, be able to jam the breaks on with leading edge if required, and flop forward only if necessary. That's how most guys do it and it doesn't require a huge amount of flexibility... just basic flexibility...
Here's a few good examples from Bobrovsky last year. He's in the midst of his trailing leg push, so his leading knee is on the ice first (his trailing knee would start baring weight next, so that he could lift his leading knee if he needed to stretch any further)... but the point is look at the groin, that's nowhere near a splits. It isn't required, and in any case it limits what you can do next because if you don't have either knee bearing weight, so you can't edge anymore.
^ look at this one, groin is a pretty comfortable 90 degrees
^ This one isn't full stretch yet, if he needs to, trailing knee goes down and leading knee rises slightly to kick toward post (as below). Plus if McAvoy makes the cut, trailing knee takes weight, leading skate edges in and he's ready to push the opposite way. This requires F'N HUGE POWER in your hips and groin, but not necessarily flexibility.
^ Here he's at his limit, trailing knee is down, but leading knee is up... you can't see it because of the way pads work these days (they are on very loose), but his leading leg is fully straight from ankle to hip and his hip is still 6-12" off the ice... ie not splits.