well, that's manga/anime for you
some character can get superstrong all the sudden

But... Roshi is always strong what, he even blew up the moon during the tenkaichi budokai waaay before the arrival of the Saiyan


Also, making Picolo & Gohan weaker is on purpose one, this is mainly the showdown between Goku and Freeza
If Gohan can go toe to toe with Freeza then no fun already, no need for Goku to save the day again

Also too bad they killed off Freeza again, since he still haven't reach his ultimate form, his Golden form are still incomplete yet as he still haven't get used to it as per Goku, hence he got his ass kicked after a prolonged battle.

Would be nice if he survived, trained harder to complete his ultimate form and come back for revenge again