Except you never needed a full 40 man of top tier players/specs even in Vanilla outside of maybe Naxx and it’s not like the “meme” specs bring nothing.
A DPS Shaman still brings Totems and Chain Heal. A Ret Pally still brings Blessings and can Cleanse and Heal. A Shadow Priest brings Shadow Weaving and VE, etc. If you have people in your Guild who like those specs there’s no reason to skip over them to fill out the last 10 or so slots in a 40 man Raid in Classic.
The tuning was always loose back then and it seems it’s even more so now.