Not all ESPs force unsubscribe links. We ultimately put liability on our customers for CAN-SPAM compliance. We had CAN-SPAM compliance checks on by default, but they could be disabled. As to your original question, no, ESPs have not gained much in the way of power. I might be in the minority in my industry, but I think this is good. All of the arguments against page-based ads can be used against email-based ads. But in this case, the users have won, and have full power over their inbox.
A couple years ago, I looked at switching from an in-house email server to an ESP -- MailChimp being one. Right as I was performing the cost-benefit, two things happened:
As a minor dealbreaker, ESP's force mandatory unsubscribe links for CAN-SPAM compliance, no matter how small/private your list becomes.[1] http://arstechnica.com/information-technology/2013/12/gmail-...