The sr swings were there because the matchmaking was loose dude. Since barely people played on the ptr the MM matched people from gm to gold just to get games going.
Periodically, there are calls on the forums for all MMR/SR information to be wiped and to start over. The justification here is that because the system has had many flaws, and that MMR/SR takes a very large number of games to move, and that people are misplaced by 250 to 500 SR (see previous section), that it would be good to wipe everything and start over. The chief problem with this is that before the wipe, the typical error is +/- 250 SR, with +/- 500 SR in extreme cases. Immediately after the wipe, the typical error would be +/- 2500, as everyone would have the same rating. Top 500 would be playing against bottom 500. This would cause matchmaking and rating quality to fall through the floor until a sufficient number of games are played. And because many people do not play a huge number of games, or play inconsistently, this inaccuracy would persist for months. And at the end of that, the accuracy would be similar to what it was before the reset, because the underlying system has not changed. My reasoning against a reset is similar to that given by Scott12.