I'll say it outright!
I'd say there are only 2 Franchise goalies in the NHL right now, and Demko is not one of them.
They are
Vasilevski and
Shestyorkin and thats it!
there are a handful of 'Elite' #1's and I wouldnt call Demko one of those either, but, he can get there.
He's a solid #1 who can single handedly win a game, and has plenty of Potential, but, he's also 26, not 23 line a Carter Hart, who can look awesome or bad, similar to Demko.
I'd say he's more like an Anderson (pre- Carolina) or a Markstrom who i'm sure you are familiar with. neither is a franchise goalie either.
a similar if opposite example would be Campbell, he's not Elite, but, he had the hot start and had some of the best numbers in the NHL, then his game fell off a cliff and now he barely looks like a #1.
A franchise goalie does not have 8-10 'bad' games in a row.
I'd say
Oettinger and
Swayman have higher ceilings as an example.