There is so much to do in this game that...

[Jojoya]

The point here is that grinds can be good when they are in a vacuum. The game has done a very good job of not gating players out of content with a grind. Where the game design is flawed is removing grinds completely out of optional "in a vacuum" content.

Which grinds were removed that were completely optional and "in a vacuum"?

I think most players would disagree the relic weapon grinds are "in a vacuum" if that's what you're thinking about. You're talking about a weapon that is generally BiS once the final stage is completed. Even the current stage is giving players access to a 630 weapon, which is the best a player can get without doing some form of raiding.

All the grinds "in a vacuum" that I can think of still exist.