Your point about having only a few curators with effective voting power is one of the potentials I see for the delegation purchase business (if and only if the blockchain rewarded good curation to a reasonable level).
If someone thinks they are a good curator, but can't afford to sink a lot of money into SP (or just doesn't want to risk too much before they know how it's going to turn out), they could purchase a delegation and see how it goes. This creates more curators with the ability to move the needle on a post. But under current rules, it's not profitable to do that.
Thanks for he reply. COmpletely see the potential you see in regards to users being able to purchase or lease SP. Granted my speculation is that you'd still have to have deep pockets and or whale friend backup in order to even make a dent in the curation game. Making it more profitable to curate could help with this but may favour early adopters over newcoming authors, hard to predict fully how that would all pan out.