No. Big surges of activity on launches / patches and big declines of activity after that only started in WoD and continued in Legion. Cata and prior expansions had no noticeable declines at all. MoP had a very slight decline that was about a third of a way from "no decline" to "big decline the scale of WoD / Legion".
The "it's seasonal" (c) Ion was not the case before WoD, someone somewhere maybe was "seasonal" but this was unnoticeable on aggregate measures.