I think part of what gets me about it is that the whole mechanic is just so unnecessary. It has the issue of being so strong that it makes any part of the (already easy) game that uses them even EASIER as you can just hit dynamax, and mash A to win. BESIDES the Gigamax forms, it's ridiculously boring in that it's "let's make the pokemon big" and then you win. It's not really inspired. Then you have the Gigantamax forms, which I love aesthetically, but... They could have just been Megas, which would further solidify the mechanic as a series staple, and also added some great designs to that cast, like the one Kingler has. It would have given a lot of Pokemon buffs that would have brought them back to the game, much as someone like Mawile or Sableye did. They don't change anything besides their form and a move, and after three turns, that's it.
I know it won't happen, but I would love if they kept doing Megas for the remake games. Like if DP's remake and BW got them, that'd be a really cool feature of that side of the core games. Of course, it's Pokemon and they love discarding things after one or two games despite a lot of them getting positive feedback.