If we're going to judge every young player on his own merits, then he has to do something to merit attention....
Powell and Brathwaite haven't merited attention yet. Also, I think it's foolhardy of you to dismiss the Marshall experience out of hand, and I'm quite relieved you're not a selector. Or at least, I hope you're not!
As for Barath, I was prepared to wait, and if you'd actually paid attention to my posts, I did say at the time that Barath was selected at the right time to play Bangladesh. Of course, we all know what happened then....
The selectors were right to make Barath wait, and they should do the same to Brathwaite and Powell. Let them wait until they're ready. Right now, they're not yet ready for regular WI duties. Maybe the occasional ODI cameo, but that's it, at this stage.