I wouldn't be too quick to blame the removal of dxp weekends on this. Especially since new bugs in the duel arena popped up on may 25th. The playercount actually went up on may 13th. You are right, it has dropped since.
Some people indeed did that, including myself. But if we go by that logic, someone that wanted to level up a skill that doesn't require supplies, he wouldn't be playing during the week. Most people that got maxed literally twice as fast couldn't care less about dxp weekends since they'd no longer be training.
I've talked to quite a lot of people about the daily task system and people seemed pretty positive about it. I myself am more fond of it than dxp weekends. It takes some getting used to, but you get plenty of dxp if you complete all your daily tasks. Playing more literally gets you more dxp, that's something I quite like.
One of the many reason staff Thomy saw the removal of dxp "obligatory"
That being said, it has ruined training certain skills with dxp completely. Slayer and farming are kind of a waste with dxp since you spend an extensive amount of time not getting exp. Runecrafting is still in an unacceptable state. That is something I dislike.
If the weekends are to return (which I wouldn't mind) then they should be more restricted. It wouldn't be a bad thing to sink a bunch of items and in return get a dxp weekend. This is just an idea though, don't take it too seriously.