Why not? Seems fair to me. If you have two clients with similar needs do you give more attention to the client that pays the least to your enterprise?
So, your position is that since Bill and Hillary have engaged in a decades long conspiracy, then everyone must be doing the same?
And your suggestion that a consultant might devote more time to a client to whom they are billing more hours, well, that’s what called a tautology.
As for the honesty and integrity with which a consultant deal with clients of any size is or ought to be identical. That’s basic.