I have to wonder if it's really a knock on Brad to have used Bradley as the main PG for four games if you consider how long Doc took to arrive at that conclusion, and to once again put him in that role after Rondo went down (coming off an injury that made him miss half the season no less).
So yeah, I don't think that it took him 4 games criticism holds any water at all.
Never mind that it's more complicated than "Bradley can't run the point". Fact of the matter is, if Bradley CAN hold his own, that allows you to play JG at the two and have him on the floor at the same time as Wallace.
Bradley was horrendous at PG, but he was a summer removed from having to do it on the fly last season. Under the circumstances, it's worth trying it out if you're Brad Stevens. Crawford is a better handler, but he's a minus defender.
The experiment failed, but that's OK, that's what this season is for. Maybe AB will eventually become passable at the job.
This^ captures my take on it perfectly.
This (playing guys out of position, in particular at 'smaller' positions) is not something only the C's have been trying out. OKC did it to turn Westbrook into a passable point. Orlando is doing it with Oladipo. Other teams have tried it out here and there, with other players, with mixed results.
If it works, you get a way to put a size advantage out on the court (in this case, not with AB himself, but with the ability to slide JG over).
If not, you slide everyone back to their normal spots and if nothing else you gave your 'experiment' some heavy experience in ball-handling that may benefit down the road even when not playing point.
And, as you say, AB is still very, very young ( at just under 23, he's the 4th youngest on the team behind Pressey, Olynyk and Sullinger). He could still eventually become passable at point down the road, as he becomes more experienced.