I'll say it:
Paid retainers are a P2W aspect. No matter how big or small. When you can have ventures twice as many times by paying, no matter how small the fee or the reward, it's P2W and it needs to go, it doesn't belong in a P2P game.
4 Retainers max, 2 default, 2 paid with GIL, not irl currency. That's how I would see it perfectly set up. Maybe 1m gil for 3rd retainer, 10m gil for the 4th retainer.
I just hate having my inventories always full with stuff and the possibility that people are spamming ventures twice as many times as me just because I don't wanna spend 4 euros more. It's not even about the money, it's about the principle.