Lavine doesn't play much defense, same as Markeneen. So I agree with some of our posters that bringing them in doesn't make us that much better.
Now the major unknown in that equation is one Marvin Bagley, as Bajaden said above, none of us has seen what this kid can really do. And that would be a major disservice to ship him out without assessing the goods. And it's also a bit unfair, with Mr. Youngman's note in mind, to classify him "soft" or injury-prone. With his athletic ability and gifted physicality, he could really turn into the modern big man who can stretch the floor, plays both inside and out (we already saw a glimpse of his ability inside, even with just his left hand), plays a mean pick and roll with Fox/Hield/Bog, and be a difference maker on the defensive end (which is the biggest question mark but you'd be careless to rule him out on that completely).
That's very different from some of the rookies/young players in the league who the critics think to have very high potential yet needs time. Bagley in this stage has already shown us he can be a 20/10 guy easily (barring injury). As I said, it wouldn't be wise to not give him another year at least to see his progression.