If this were a URG, and it’s not, I wouldn’t recommend this unless the property tells you they’re completely sold out AND they refuse to reaccommodate you as per the rules of the URG. Since this was a room type guarantee, staying in the downgraded room and demanding comp prior to departure was your only recourse. I think you did pretty well at 50000 MR points (est. value of $450 according to NerdWallet). Also, I’m not one to take a property, or even Marriott’s side on these issues, but the T+C are pretty clear. The only way this is a URG is if you made a reservation, you arrive at the property, and the property states there’s “no room at the inn.” You had a room (or two rooms even) based on your posts above; thus, there isn’t much more Marriott can (or will) do even if you take it up to “Mr. Marriott’s Office.”

P.S. Placed in a situation where I wanted a suite and none were available I check in, I’d ask the property to cancel my reservation and I’d re-book elsewhere. Doesn’t qualify for a room-type guarantee, but I would be happier because I have my suite. Obviously, this is not always practical, especially at the last minute. I suppose after reading both of my posts, you should ask yourself whether you and your daughter had a good time in London despite the room situation. If so, then I’d conserve your time and energy towards something else. Just my six pence as someone who was exactly where you were albeit at a different property that was shut down because it didn’t pay their taxes. YMMV.