I think part of the reason they come across as mediocre to modern ears is that they were so influential, basically every rock and pop singer copied them. As such, they can easily come across as generic nowadays.

If you want to make a fair comparison, look at their work compared to every other artist at that time. If you're judging them based on current music, or even stuff from 40+ years ago, then you are literally comparing them to everyone whose music was influenced by them. There is a lot of musical style that wouldn't even exist today if not for them.

Whew, are you looking to get downvotes into an abyss?

Also, what the what? Yesterday, Eleanor Rigby, Hey Jude, Norwegian Wood, there's dozens of songs that are classics because of the lyrics, even if nothing else was well done.

I get it though, not every big band/performer is going to "click" for everyone. No hate here, my homie