If the sponsorship is not for the link, then why should the link be devalued?
Irrelevant. The focus is the sponsorship, not the link juice.
Of course the link has value. But that's not what is being bought (sponsored). Any value from the link is incidental to the sponsorship.
Google is not preventing anyone from following the link to the sponsor's site. The visitors still flow, even if juice doesn't. Visitors still see the sponsor's name.
I can understand your wanting to "add value" to the sponsorship by providing something above and beyond what they are buying. But too much obsessing can be harmful. Not just for your mental health, but by Google figuring out that you are trying to "deceive" their algo.