I'm missing something. What alt problem? Don't they know only 1 character can log at any one time?
Wintrading can be done (and usually is) between 2 players. Cheaters don't need to make another account
when both can rank up.

Decay okay for queues. They are right the numbers will go down but out of numbness, not because its alts.
Who will go numb first? Real players with full time fight or the wintraders who doesn't need to go all out.