The problem with Romeo is that when he was drafted he was years away from being an NBA player. He was also drafted by a team that has not, at any point during Romeo's time on the roster, been especially invested in trying to develop young players. So now we're in the third season of his rookie deal and he's showing signs of being an NBA player, but he's still very, very limited.
Maybe in a few more years, in the right situation, Romeo will have a more significant and varied role. But for now, he's shown that he can be the 5th guy on the floor, hit some open shots, finish some fast break plays, and not be a weak point on defense. That's a positive piece to have, but as Lowe points out, pretty disappointing for a lottery pick.
Danny went for upside but unfortunately he either underestimated just how raw Romeo was or he overestimated how quickly Romeo would develop.
As to the latter point, Romeo has been injured a lot in his first couple of seasons, which has put a damper on his development. But of course, being in physical shape to avoid frequent nagging injuries is part of being "ready" for the NBA.