If you're really curious and want to know tho, I went from rank 17 to rank 40 in less than 2 weeks but that was with doing FL back to back queues and winning most games with about a 67% overall ratio at that time. WD I hardly ever got a pop and when I did it went 7/8 and some scrub didn't accept the queue and I had to wait another 10-15 minutes for another just to get the same failed pop. just don't waste your time with WD. you'll prolly get 1 pop an hour, if that many and I don't remember how much XP you get at rank 21 per win solo. but i'm sure its nowhere near the amount you get for two to three FL games in 1 hour that you'd get a few hundred points in XP whether win or lose.

if WD did pop back to back though, it would grant more points but just because no one really does it anymore, you won't get as many games per hour like you would FL. I guesstimate that currently if you tried to level from rank 21 to 40 doing only WD, it would take you about a month or so.