Here is why I feel they are.
It’s similar a level 50 character in an MMO to try and take down a level 65 raid. On the flip side, anyone with a good leader can just put any random 6* on an attack team and just blindly kill.
Tyreese and Yumi, both blue, can easily shred a Priya/Zeke/SHiva team without even rushing or having active skills.
The comparison of 5-4 vs. 6-5 forexample. For first year of meta, using 5 and 4 was a viable strategy. I was in a 1st place faction and winning wars and getting mulitple defends using a really good 4* and the rest 5* (Zachary during the Andrea meta)
That was still the case with 6 as great 5* were viable on defense, but now it doesn’t seem like it. If I can kill 2 Priyas using blues and no AR, that’s just too easy and ruins all the work people put into building a defense