I think hax training gains are fine, but it's the way they just throw it in that makes them retarded. A show is boring if everyone is absolutely useless except for the main character and all (which is a large reason why GT/FNF/etc. were such horrible failures), so I don't mind people gaining ridiculous increases to catch up, but if it looks like they had the option of doing that and they just basically sat on their asses not taking that option to remain weak for as long as the plot didn't demand them to be strong, that's a problem. Freeza basically couldn't be arsed to train for 3 days to surpass Goku despite losing most of his body in the battle and being spared, and Piccolo could train for like 5 months and catch up to the God Saiyans' base forms and then some, but just sat on his ass after the Cell Games doing menial training and stuff. All of that just makes the boosts seem inconsistent and spontaneous, only being thrown in as poor explanations when the author couldn't think of new characters to shine so he brought back old ones with super astronomical increases saying they trained off-screen.
Just extremely poor creativity and consistency really, even if Toriyama's said he stopped giving a shit about that during the Freeza movie :1down
