Yeah, anything past the 80 knots/1000 footers would be kinda difficult to develop an ROT, certainly with enough accuracy to be confident telling the CA that some is wrong at V1-10.
More better anyway to have a good reasonable-ness check beforehand during your setup, and I bet most of us have a better sense for that than we think, especially with airports we go to all the time. Like, if the 1s are open in SFO, and I was loaded up with full seats and gas for a transcon, and somehow I got numbers for a flaps 5 takeoff, I’d be taking another look. On the Vr thing, I hadn’t noticed that, but generally it seems like usually flaps 5 your V2 is in the vicinity of GW/1000.
I think most of us actually have a pretty good spidey sense for these things, but can get better with a little practice and help trap these errors.