I totally agree with your findings !!
For two years ago, I made the same jouney to "replace" my old HD-480 Classic.
As a producer and radio jock, I thought it was easy to upgrade my old Sennheiser, because technology runs fast over the last 20 years :-)
So I tested the "alternatives": Beyer Dynamic DT-770 Pro, Beyer Dynamic DT 990 Pro, Sennheiser HD-598, Sennheiser HD-25, Sennheiser HD-595.
With this panel it should be easy to finally find a good successor.
Although they're all good headphones, none of them was able to beat the sound of the "Classic One".
Beyer Dynamics have (as mentioned) a real good bass, but a "headache hights".
The 595 and 598 series Sennheiser showed a good bass but with higher volumes they deformed the bass, while the HD-480 Classic keeps playing without any disortion...flawless.
They produced a better high for my ears like the Beyers but still too much and tried to compensate it with the sound control on the amplifier without success.
The only good alternative was the Sennehiser HD-25, but I missed the open ear system (use it in the studio without background sounds and noise)
I finally returned all others and after a long search for almost 1.5 years, I bought (hard to find) spareparts to (re) build a new HD-480 Classic headphone and a spare one to be safe for the next years.
Be aware..... those tested headphones are all "best in class" , really good performers and best bang for buck. I really can reccommend them if you don't have a HD-480 Classic around you :-)
But in a direct comparisation with the "Classic" they were unfortunately no match.
Finally I'm a happy funkateer :-)