Well, if it's sort of wrong to say one spouse pays purely at the higher rate, then it's also sort of wrong to say the other spouse is paying at a "much lower" rate overall than they would if filing as a single. For example, if you have one spouse earning $230k a year, and another earning $110k (both considered "high income earners"), they would be paying several thousand more in 2016 filing jointly than they would filing as single (using an online calculator, it came out to around $13k difference in Fed taxes plus FICA). For me, anything over $1k is a substantial penalty.
Under the trump plan, the brackets are reduced to 10, 25 and 35 percent for both single and married filers. We don't know how income will pass through those brackets (surprise, surprise, no specifics), but I'm willing to bet given those brackets the marriage penalty increases, and the effective rate goes up for both.
I don't really disagree with anything else you clarified/corrected, except that in my household, the marriage penalty is substantial enough that it definitely plays a role in determining whether it is worthwhile for both spouses to work (in addition to childcare expenses and sanity like you note). I get that's a personal thing, though, if it doesn't influence you one way or the other.