It is a poor value trade.  White is better and given what Boston gave up to get him, they can't make that type of a trade for a guy that basically no one wanted last summer.  Plus, I don't think he makes Boston better than keeping White, and I'd honestly trust someone like Dwight Howard more to be a spot starter at center than someone like Markkanen.
White is better if we count both sides of the ball, offense, and defense... Markkanen is a poor defender...
 He's better on defense than you probably think.  White is the better defender overall,   but he's 7 feet and he can jump, he's made a lot of impressive blocks on excellent talent and length in the league. 
 Blocks that D white just simply cannot make. Plus with Horford about to rapidly decline I think it's a no Brainerd if Brogdon stays healthy  
 When you factor in how much better Lauri is offensively,  reliable,  consistent three point shooter with a much better career percentage,  plus the fact he's seven feet tall. 
 Another thing he does consistently is dunk on the best players slash longest players  in the league