Should each team be allowed to keep one player for atleast 2 max contracts length ?

Well said. The problem for teams like the Bucks isn't only that they're small, but that they also aren't managed terribly well. Other teams like Indiana are managed well (and some like Cleveland are lucky). Meanwhile, teams that should be attractive destinations have gone long periods of time not being so because they've not been managed well -- the Clippers were a pariah until they got Paul; the Warriors being in the Bay Area should have been a draw; and Philadelphia should be bigtime as the 4th largest media market in the country.

On the flipside, there does seem to be some mega-markets that are coasting. The Knicks catch way too many breaks for being in New York despite terrible leadership. And the Lakers will probably do better than they should in the coming post-Buss years just because players want to wear a Lakers jersey.

In any case, I think the solution has something to do with increasing the front office professionalism of the perennially bad franchises. Something like a franchise tag does the opposite -- gives bad franchises a crutch to keep being bad at managing.