So regarding the whole Hassan thing, what we're seeing lacking are the things that a certain Ekpe Udoh does in an elite fashion. No secret that I've pined for Udoh being the primary backup since forever, and have advocated that multiple off-seasons. Everything you want from Rudy in terms of having the defense run the same way is possible with Udoh than pretty much anyone else I can think of in the league. Udoh can protect the rim and gets blocks, but it's his rotations and agility, as well as his ability to step out to the perimeter, that make him the perfect fit in that regard. The biggest challenge with Udoh is his severe offensive limitations (which wouldn't be as big of an issue with how we're presently constituted) and also his horrible rebounding (which would be an issue). Those are the things Udoh gives you that Whiteside does not (and that Favors does not). On the other end of this, what Hassan does that Udoh doesn't is actually quite a significant difference. Whiteside's rebounding percentage is typically about twice that of Udoh's, and with our current makeup that's a big deal. Whiteside being able to catch a pass and have a body on him and his offense is overall worlds better, even if you're not running anything for Whiteside and even if you don't want him having much usage. Whiteside isn't really spacing things per se, but his presence will keep the defense a lot more honest than Udoh. So if you're not willing to stomach the extreme of going to Udoh, Whiteside offers a good compromise between Favors and Udoh. You probably won't change a lot of his instant instincts to any significant degree, but I believe he can fit in with his physical profile to being able to play more the style that we're looking for than Favors physical profile allowed. The rebounding and attention from the defense (relative to Favors) provides a bit of extra sauce.
tl;dr I think Whitesidee can come in and check most the boxes of adequacy. The comparison is with our alternatives and not with Rudy. I think he'll adapt to a degree and his defensive style will approach what we need more so than it does now (not entirely). Dwight Howard was my other underrated alternative.