Arenas were most likely more active on retail. That should have prevented targeted wintrading and other similar activities. And as far as I know, mmr system here is still not fully blizz-like. I don't think it was ever possible to use mmr dropping to achieve higher rating on retail.
it was only "kinda" possible in 3v3
where 1 person was around 2700 mmr
the other two were at around 1600 mmr
so you could face 2100-2300 teams. but still get 10 to 25 pts per game

then again after about 5 to 6 games the two that were 1600 mmr are now caught up to the 2400 bracket so you'd face 2600 to 2700 teams again. and you'd get a maximum of about 150, maybe 180 rating for beating low teams.

the punishment for losing was intense tho. cus the person who was 2700 could lose about 200 rating with 1 loss