The Bam motor thing I don't completely agree with. He played with great motor against the Bucks, but I've tuned into a number of Heat games (playoffs and not) throughout the years and been unimpressed with his effort level. Maybe he is the type of player who can turn it on and off, but I'm not sure I'd call that a good motor.
Rob definitely has some court vision for passing like Bam, but what no one (except the Heat?) saw was the way Bam would develop a comfort handling the ball. He brings the ball up the court quite a bit and initiates the offense. Many of the plays he is involved in are similar to the Celtics' sets with high DHOs, pnrs, and swinging the ball, but Bam has develop a few 1-3 dribble moves, spins, and even the occasional eurostep. His offensive versatility is continuing to grow.
Rob has never demonstrated these yet in a game. I think he is far more satisfied to be a distributor and rim-runner. Honestly, that's probably the kind of big man we want, because we want the ball in Tatum, Brown, Hayward, and Walker's hands to make plays.
Defensively, both have a lot of mental lapses. Bam has grown in this and is much better than Rob, but watching many of their games have made me question how good of a defender he actually is. Rob still has a ways to go in his rotations, but has demonstrated some encouraging signs throughout the playoffs. I think Rob is a little better defending pull-ups and mid-range because ball-handlers don't really realize how long and quick off his feet he is. Bam has also demonstrated a lot more consistency on switches against all kinds of scorers.
I agree with other posters that expecting Rob to be as good as Bam in this series or even if his career is probably setting yourself up for disappointment. A better question is whether or not he can hold his own against players like Bam and contribute to the team winning over Bam's team. I mean, if we can win the matchups against 3-4 of the starters, and Rob becomes the starter at center and can hold his own, then we will win many games.