The new voices are bad
I'm not a Justin defender (and 100% support firing him), but I hate that no one is willing to admit how skilled and irreplaceable of a voice actor he was, just because he's now persona non grata.
The new Rick voice is especially bad and sounds so flat and brain dead to the point that I find I'm excluding those episodes from rewatches. Justin's version could be could be rough or soft with a wide emotional range, making the character audibly feel real and not cartoony. Perhaps the only similar voice acting that elevated the character to such an extent is Christian Bale in Howl's Moving Castle. Justin also used stuttering, burping, and other sounds in novel ways.
Even the closest impersonator, Sean Kelly (who was praised by Justin himself) can't quite capture the full complexity of either Rick or Morty. And the anime Japanese/English voices are miles away in all aspects.
I also find it hard to believe that Justin had zero creative input in later seasons. Even if we wasn't in the writers' room, it's not difficult to imagine that he improvised jokes or line delivery while recording. The ending to the two crows episode (“shows on your shoes”) is 100% improvised Justin style but passed the time when he supposedly stopped contributing to writing.