I don't think they would expect to win titles with that tandem. It is just to get them going in the right direction in order to build a title contender.
You're way too concerned about his passing numbers for a center. Are they low? Yes? Do I care? Hell no
Exactly. If everything falls perfectly in place and the Lakers manage to pull off getting Durant and Whiteside and then somehow get Westbrook the next year (as some have crazily suggested), then they could be back in title contention almost immediately.
However, assuming the above doesn't happen, which I seriously doubt it will, then I don't think Whiteside/DeRozan would be a bad step in moving back towards relevancy.
It would remind me of the 90's rebuild when they went through guys like Vlade Divac, Elden Campbell, Eddie Jones and Nick Van Exel to get back into the playoffs. That ended up leading to Shaq/Kobe. None of those guys were still with the team when the Lakers started winning championships, but I don't think the 5 titles in the 2000's happen without them having been on the team.