Point taken.
Would that assertion be consistent with player activity levels you've collected?
Assuming you've collected data across that time span and assuming that increased player activity is possibly indicative of increased "fun" and engagement. (I guess people not having "fun" would stop playing as often whether they are subscribed or not.
I have collected that data, but I'm stepping on thin ice here. There is too much speculation involved, for we don't (and never will now) the percentage of players are on trial v subscription, what other factors do have on influence on player numbers (advertisement, competition, economy and so on)
That being said, there is no indication that things have been different than HT stated

After the split we had a considerable increase in "active players" and even more in kills (as a measure of activity). Only about 2.5 years later numbers started to drop - IMHO way too long of a time that it could have been because of the arena split itself.
(More on arena populations and general player activity in the upcoming "AH stats 2010"

)