I hope this example helps.

The voting efficiency is not comparable to the ROI on a lease.

Example: my voting efficiency is 73%.

The amount of SP that will earn me is 458 SP.

That would be 23816SP per year if I can keep that up.

I'm currently voting with a 175k SP stake.

My voting ROI on curating is therefor (23816*100)/175000 = currently 13,6%.

This number is comparable to a lease.

Currently, it makes no sense for me to take on a lease, but it does make sense to lease to anyone offering more than 14% unless I can get better at curating.