They would just find a way to adjust to it to maximize their ROI so I doubt that changing it wouldn't change a thing in the end.
Indeed, but the point of aligning incentives is to achieve the situation whereby participants following their self interest (maximizing ROI might be the strongest of that category) the system benefits from the actions they take. That's the goal in applying game theory.
Making it in a whale's (and everyone else's) self interest to keep their SP in one place has the effect of highlighting their actions more clearly and opening them up to scrutiny. This scrutiny is one of the best features of this blockchain and an often unacknowledged reason why things are the way they are. Implementing n^1.2 implements a cost for whales who want to disguise their activities in obscure alt accounts.
Regarding rewards, I'm a firm proponent of rewarding those with stake or who are able to appeal to those with stake. Any other system is not Steem, it's some kind of welfare.