"Dragon Ball started to slip because there were no drawbacks to characters after a certain point. You had character flaws, certainly— most (in)famously, Vegeta's hubris, Gohan's overconfidence, Gotenks' juvenile naivete, and Future Trunks' lack of battle experience and overzealousness. You could use these to take down these characters if you knew what you were doing, as Cell did with Vegeta and Trunks and Boo did with Gohan and Gotenks. But these were weaknesses that could be permanently overcome unlike, say, kryptonite. Again, that wouldn't be a problem in an underdog story with a single arc or in a story where certain characters have certain abilities that other characters don't so they can complement each other (i.e. the 5 Man Band), but Dragon Ball isn't that. Thus, there wasn't much else to really hold back characters, and it really showed in Super. Badly. Because even though Vegeta changed as a character (which is good), he also lost his only heel that villains could use to reasonably defeat him, and yet he still kept losing because the plot demanded it. Goku's only weaknesses before now were hunger and his tail, but hunger stopped playing a role when the series became serious and he permanently lost his tail after Kami pulled it off, so that was that basically. Beyond that point, the only weakness in the series was "you're literally physically weaker than your opponent", and when that happens, you basically reach supercritical mass of anime escalation."
This supernova of faggotry might actually know a thing or two.