Ehh what are we comparing this to?
If we just take the SS ladder and compare it to the 3v3 ladder in MoP s15 for example, there were 100k more characters in MoP compared to now, and the SS ladder shows people with 1 round where the MoP ladder only counted people above 1k rating.
End of WoD still had 3k more characters than current SS ladder, same 1k rating cutoff to count
It is worth mentioning that both of these expansions had significantly higher sub counts, however
Legion was a relatively popular expansion so hard to say whether PvP was more or less popular. I’m sure most would argue that it’s definitely more popular currently than it was in BFA, though some will argue that it’s not more popular than first half of SL especially
Numbers compared to DF are very similar which suggests it’s at the very least not growing