I think the Q is actually the biggest step up. The physicality and defending isn't at the level of the WHL and OHL, only reason the gap wasn't massive for MacKinnon is that he probably entered the league and immediately became the best skater in it (or atleast top 5, similar to McDavid this year, but McDavid's IQ is on a whole other level). Its more realistic to look at the path of Drouin or Huberdeau.
The OHL probably has the most guys who can immediately make the jump, but I also think they have by-far the largest pool of talent, so top guys coming out of there are top guys. Not trying to say Ontario has the best players, but I think the OHL unlike the WHL and especially the Q, has had great success of pulling in USNDP guys and Americans in general, making a deeper league. The States the OHL draws from tend to be more willing to play in the CHL, while also being high-quality talent wise (NY, Michigan, Wisc, Pennsylvania and Missouri). Whereas for you guys pulling top kids out of Minnesota (as New England is for the Q) is near impossible and even some of your own best talent goes NCAA (Toews, Fabbro, Schwartz, Kariya, etc).
Weirdly, the WHL just hasn't had that elite #1 guy recently, RNH did well in his transition but has had his development stutter. Also, it seems the best products out the WHL in recent years tend to be D, who will always take longer (Jones, Murray, Rielly). Drai and Reinhart both looked pretty good this year in their D+2.
Either way, I'm excited to follow Patrick this year. I know by the time the draft comes around people won't be talking about him being a bad 1st overall, I just hope its for the reason he proved his doubters wrong, and not general draft hype. My guess is he enters the draft in the same tier as Hall and Seguin and slightly behind the Eichel, Stamkos, Matthews, and Tavares, and maybe on level with Mackinnon. I'm also not heavily weighting the memorial cup, it is just one of the better viewings (video quality wise) I've had, as I hate streaming games on a comp, so I mostly watch the QMJHL and OHL games I regularly get on my cable package (luckily, it seems I'm going to get a lot of Veleno games this year). So, I'm clearly hoping he gets on the WJC team, and Sportsnet picks up a couple of his Friday night games.
I feel a smart coach will break him in on a sheltered 3rd line that is used offensively, the game is changing to a top 9 with a grinder on each line than a classic Top 6, checking line and energy line.