It is an interesting topic. White has made it a topic of discussion by playing so well. Think back one year ago though. White was in a funk, couldn't hit the side of a barn. Meanwhile, Smart was the floor general for the best starting 5 in the game, and playing some of the best basketball of his career.
My point is that it is wrong, or at least incomplete, if you only compare what Smart and White have done in the last couple of weeks. In that time, White is playing the best ball of his career, Smart is coming off an injury and is not playing the best basketball of his career (to put it mildly). At some point, if both continue on their current trajectory, then for that hypothetical, I would say yes, White should be bumped up to the lead PG and Smart should find a bench role.
But I say give Smart some more time. See if he can get his mojo back. Time is running out on the season but I say give Smart two more weeks, until mid-March. If at that time, White is still playing that much better, then yes, make some adjustments and prepare for the playoffs based on that.