Self-sufficiency doesn't negate P2W so I don't get why it's being brought up.

I used to play a game where all players were technically able to get everything. Cash shop items could be acquired from events (or by buying from cash players).
However to do so the free way could takes months-years for an upgrade, whereas the cash players would be able to do it as soon as their wallets allowed (within hours).

Now of course what we're seeing here is NOWHERE near that bad. But the point is that just because a player can indeed earn that gil, doesn't change that it'll be faster for a person under the same circumstances (same playtime, same types of items to sell, etc..) to get the gil they want.