Yeah, but the issue is that if they grow in power in base form and go beyond SSJ in base, then SSJ ends up being stronger than it was originally, same for SSJ2, etc...
Like, if you have base Goku at over 150 million in the Buu arc, then x50 that and he is already in initial SSJ2 tier realms.
The stronger they get in base, even if over initial SSJ, just makes SSJ all the stronger so as long as base grows, nothing stops SSJ from surpassing even SSJ3+ eventually. Some people dont like that thought.