I agree with your premise and wouldn't personally do it. However, I don't think these situations are quite as taboo or quasi-pedophlic as you categorize them to be. It is acceptable depending on the context of that relationship, or as you place it: power dynamics.

Power dynamics is dependent on: If they are both two consenting adults who are financially and emotionally independent & stable of each other. If those conditions check out, then there really isn't much of a problem, and it doesn't qualify as quasi-pedophlic sexual predatory as you seem to be painting these relationships or sexual encounters to be.

I mean, I've met couples - with children - who are 19/28 & 23/31 and started out which way. These relationships do happen.

I concede it is weird, at first glance, or when it's like a 30+ year old who exclusively dates teenagers/undergraduates. Yet people involved in those age ranges are still adults with their full agency behind their actions when they consent to sexual intercourse or romantic engagements; if both partners are financially, socially, and emotionally stable and independent of one another, then categorizing this as creepy, weird, or quasi-pedophilic , feels dehumanizing and infantilizing to reduce teenaged adults into helpless victims of those elder partners.