there is certainly a difference in player pool capability as we move up in stakes but a larger factor would be how big the fields are to begin with. These are my personal takes on the subject:
An $11 3k gtd with an average of 500 players in it should be much easier to win than a $2.20 4k gtd with 1600 players simply because we don't have to fade that additional variance - even though the $11 game will likely have a few more skilled players in it.
Through my experience freerolls and games up to $3.30 are VERRRRY similar in general population abilities - there are a few reggy small stakes grinders who are definitely good and crushing the games they play - but these are also the levels that have the most fish in the games. $5.50 and $6.60 games are also not much different beyond the $3 realm - ever so small player ability increase, generally not to recognizable - what made it stand out for me is if you play enough of these stakes you will start to see all the regs floating around and become pretty familiar with who is decent and who is not.
The $11 are where I start seeing more capable players - when you have too teir prize pools offering $800+ it draws in the sharks looking for a good ROI and good hourly rate if you are to win. Same with the $22s and I can't speak much for anything higher as I have only played a handful of those tournaments.
The good news in all this is that not all players are good annnnnd not all player practice good bankroll management - so you get shot takers in the larger (low level) buy ins just looking to hit one big score. Example :
I flopped a FH Sunday in a $22 20k with 77 on a TT7 board in a 3bet pot - all of us about 125bb effective, i opened the CO 2.5bb - SB called, BB 3bet to 11.5bb - so i called and the sb called as well.
As I said, flop was TT7 rainbow - sb checks, bb bets 14bb, i call and the sb raises to 34bb - the bb calls so i shove it in there targeting the Tx
hands and sticky overpairs -- sb snap calls and the bb calls as well.
Sb shows JTo, bb shows QQ - board runs out TT7-T-6 and it is what it is.
The point here is not a bad beat story...the point is we got JTo calling 3b pots OOP and post flop with all that action on the flop - 2 all ins in front - we STILL got QQs to call it off there. Good players are folding QQs in that spot, a good enough player may even find the fold with JT on that flop because what worse Tx hands are in a 3b pot preflop - and stacking off on a TT7 board? T9s? Thats maaaaaybe the only combo and with a T in your hand and 2 on the board there would only be one combo of that left in the deck making it HIGHLY unlikely here. So the fact is - we basically NEVER shoving worse than JT on this TT7 flop -- and we get max value from both villans in a chance to win a 370+bb pot.
In conclusion im just saying there are bad players in every buy in level and that makes the game profitable, but the skill edge in the general population pool certainly increases with buy in amounts - how much is totally dependent on the game.
Remember - game selection is key!! Winning an event in a massive field is as tough as it comes for even the best players in the world - so even tho that Sunday $6.60 25k gtd looks juicy, you're going to need to beat 3200+ players to do so - better off spending your money in a smaller field with a decent prize pool where your
odds of winning are much greater. Game selection and good BRM are key to being successful long term.
I hope this all makes sense and I hope you find it useful.