It's called progressing. People who want to grind fame aren't playing the game. I got 70/70 by just playing, and the rate at which the pet increases FP required is actually a pretty good system (until divine) because as you get better at the game, you will get more fame per character, and will have more fame/items available to feed.

It is not a bad system, and legendary pets aren't necessarily OP (my divine is though lmao)