Wtf heavy is hard, you can get away with a lot of stuff in pubs, but in comp you need game sense. Knowing when to push when to hold, sniff out spy's, be weary of sniper spy demo sentry placement, understand that your gonna be taking a lot of focus, your not gonna be the one dealing the most damage in teamfights but rather cleanup when the demo is done doing his demo thing. and a lot more. Heavy is slow, and big. His tankiness is his biggest strong point, but he his shit on his own, a good scouts soldier demo even pyro can kite him 1 v 1 and win. Just because a heavy is good in pubs mean nothing in 9v9 or 6v6 he can be damn near useless. Even if he is considered easy
I'm not sure this is about higher level play, I think he means learning the mechanics of the class for newer players..or so I gauged from the responses of other players. I'd definitely put heavy at the top of the list as far as class mechanics go, they really did take most of the skill out of it when they tightened his spray, and lowered the spinup time.
If we are to assume what can someone who has hardly ever played tf2 pick up and DO WELL (that's the keyword) my list is prob
Engy
Heavy
Pyro
Soldier
Any other order for the other shit.
The reason for engy first should be obvious. I may have put Engi behind heavy and pyro before the mini sentry addition, and the short circuit changes.
People defending heavy saying he requires placement and knowledge, one could make that argument for every last class in the game, heavy perhaps moreso...but as a whole that player could probably be doing much better putting his time into a more rewarding class, such as soldier or demoman. There isn't much difference between a great heavy, and an amazing heavy. The gap from bad to good, and good to great is there, but as far as "top tier" goes there really isn't much a gap between what one might say plat or gold heavies.
I put pyro third simply because I specified "do well" sure it's annoying to everyone when some kid with a gibus and backburner runs at us and burns us, but 90% of the time you will kill him and probably get to a healthpack / put out by team / water before you burn out. I will also say pyro is the same way...bad to good is big, good to great is big, great to amazing isn't really. Game sense is also important, but we aren't discussing game sense so much as the classes kit.
Soldier above the other classes because while the skill ceiling is huge, it's still relatively easy to pick up a rocket launcher your first time and do decent. The other classes require atleast some foresight/are low hp/etc.etc.etc.etc. to learn before you can really do well with them.
Just my two cents on the matter.