Regarding the dribble drive thing, I agree with others that it looks like Stevens wants to run a 5-out system similar to Atlanta, and having big men who can hit a spot up three or pump fake, attack the closeout, and then get to the rim or kick it out to a shooter is an important ingredient to successfully running such a system.
I don't know if Kelly has the quickness or decisiveness to regularly do that, but he's shown some ability there.
Anyway, Kelly is an efficient and productive offensive role player. His rebounding needs improvement and he could stand to be more assertive taking shots from outside. He presents as a rich man's version of Matt Bonner, which is not a diss considering that Bonner, with his limited skillset, has contributed in a very real way to multiple Finals teams.
Still, the issue for Kelly right now is that he's one of 5 or 6 guys vying for playing time as a "big" on this team. If the team doesn't see him as a significant part of the rotation moving forward, they ought to sell on him while he's still viewed as a stretch big with starting potential, rather than a guy who can't get playing time on a 45 win team.