I don't think Romeo lacks explosiveness, I think he's tentative and doesn't commit to getting to the rim.
I think his DARKO comps are interesting. First hundred games comps for DPM are: DIllon Brooks, Danny Fortson, PJ HAirston, Jared Jeffries and Tony Snell (all but Fortson were a decent amount behind Romeo at the 90-100 games mark) Box DPM adds Bruce Brown, Stauskas and Jamal Crawford.
I think Romeo is a good defender now, he has some real 3pt potential (DARKO 3pt comps are: Lonzo Ball, Keyon Dooling, Grant Williams, Jason Richardson, Quentin Richardson) I see his path to a long term NBA contributor pretty easily, he has the D, the 3 is coming along, he's a decent secondary handler, he has in the past shown some ability to get fouled. That's a solid rotation guy, and one benefit is he can guard PG, which is a spot a lot of the good 3 and D guys can't. I'd rather a bench guy who can guard 1-3 (most 3s at least) than guys who guard 3/4 (and some 2s).
Nesmith... I just don't see it, he has a lot of energy, but he can't defend, his shot is missing, he doesn't really do anything at an NBA level yet. Now he has an extra year of control, but... he's only played 15 less games than Romeo, and he's miles behind him as a player.