Exactly why they changed it, yes. Or one of the main reasons, anyway.
Well it's close enough, I'm almost 100% sure it was S2 (mid-season, I think) because I did not play serious 2's before that season hit. Played warrior/paladin and we'd always change to shadowresistence set (ridiculously good one, too, PvE parts etc so we took virtually 0 damage) if we met SP/UA lock. The DPS/healing loss was stupid, but it paid off. \o/
After this changed we continued to do the same for some months, my warrior would join instantly and due to his PC being really fast he could zoom furthest in and see through the gates, so we'd just change before the game was actually going if it was SP/UA. This got fixed too, though, unfortunately, before we could take rank 1. Sad times, sad times indeed.