I do think the speed thing is a bit overrated. There are plenty of guys who play at a high pace consistently, but are very successful doing so - guys like McDavid, Crosby and Hall spring to mind.
Whether you play consistently fast, consistently slow, or change up the pace a lot, I think the most important thing is hockey IQ. Can you find your teammates well with passes? Can you find the soft spots in the d without the puck? With the puck, can you see the seams in the d for yourself, or see how to draw opposition to you to open teammates up? Even in one-on-one scenarios, can you subtly pick up on when the defender is off balance, so you can beat them with simple but perfectly timed/thought out moves?
Guys can get by with all sorts of combinations of most - big or small, fast or slow, strong or slim, shot oriented or pass oriented, etc. Whether you play the game at Connor McDavid's lightning pace, Joe Thornton's slow pace, or are constantly mixing it up like Kane, there is one common trait shared by essentially all stars, though - they're constantly outthinking the opposition in the ways I described above. Basically all stars are WAY smarter than the average player in terms of how they see the game. If you don't have that high hockey IQ, you're basically going to max out as a decent player, but not a star, even with outstanding tools. I'd describe both McLeod and Lazar as mediocre thinkers with strong tools, I see them both being decent NHLers, but not stars. Neither are dumb players, and they both certainly outsmart(ed) their competition in juniors, but I think they'll both shake out pretty average in the hockey IQ department at the NHL level.