But some other sections on the forum like Bitcoin Technical Support, Development & Technical Discussion even meta have much of the newbies contributing in effective way. This proves that also majority of them come here to learn crypto or trade crypto.
It doesn't prove anything of the sort. ~20k new users get registered every month and ~5k become active (create posts). Few of those may end up in technical discussions. The vast majority are useless bounty-hunting shitposting dregs. You only need to open Patrol to see what's going on.
Not that it has much to do with DT. It would be nice if theymos could implement some disincentives for shitposters but for now this needs to be deal with by reporting to moderators and there are many users doing just that.