Its not really pay2win, the difference between Expert and Ace is marginal and wont let you rake up all that didnt upgrade. The Expert state is achievable with Lions so every1 can do it.
pay2win = you pay so you have an advantage over others that don't pay. It doesn't mean some1 wins automatically if you pay.
So in this case its marginally but its still pay2win.
To many people are not aware or don't handle to what P2W means. Like dogma Charlie for example: ''Yea but its just a little advantage so it is not pay 2 win ''. The ideaology is evil. P2W is having an advantage over non payers, doesn't matter how big the advantage is. With expert you have +30, with ace you have +50 on many stats, the difference is not big but notciable. And with reload speeds the p2w factor becomes a lot higher, not with the other stats as much tbh.
Pay for time is something different, But it can be exaggerating like WoT if you dont pay at all and want to play all tanks with 100% crew it takes on a (no)life time.
Pay for content/time is for example buying premium tanks/planes/ships. In WoT a premium tank is sometimes 40 or 50 Euro, if you imagine how many tanks there are in game its like paying 50 Euros for less than 1% of the tankcontent. But it has double credits.