But they are terrible, one-dimensional Mary Sues.
It's definitely to the point where one shouldn't be looking to Super for anything meaningful... it's all 100% fanservice (just not the usual kind when you talk about anime).
I disagree, but either way, not focusing on them won't fix that then. Then they're just wasted potential that Super gave up on. I don't think Gohan or anyone from the main cast should be sacrificed for them to be included into the main cast, but they should still be included into the main cast.
After this arc Super needs to dive down into Sadala, and what the issues are there that Cabba was worried about, so they can develop all 3 U6 saiyans more.
I'm glad you're upset and hope you continue to be
What lore did they even fuck up?
Frieza in hell with Cell and 50 other people was never canon.
I'll give the earrings and the saiyan in the back, but one never had a proper explanation, just a guess by Elder Kai, and the other is really no different than Gohan explaining Ki control to Videl. That never had an explanation before, so they're things that are fair game to explore, because Z never gave proper answers on them.
I guess they completely gave up on LSSJ since no one has called Kale's form LSSJ, so they'll call it something different, but Broly was never canon to begin with, so it's not really Z lore.
Most of Super is new lore being added, not lore being taken from Z.
Did Zenkai boosts in Z not fuck up a lot of DB's lore? Al lot of what Goku did to get stronger, was usually after he recovered from near death in Dragon Ball, so it could be attributed to him getting Zenkia boosts story wise.
Climbing Koran's Tower, drinking the Divine Water, nah they did fuck all, it was the Zenkai boosts created in Z.