What status quo? 1-2 points. If I fallow your logic now they can be possible quicker than MS , but after one-two races when he will be ahead of them they will never have chance to be faster than him in the same car? And this come from only 1-2 points difference in WDC. With this difference you can't make any conclusion. Or look this way 91 wins against triple 0 for Nico, Nick and Pertov. This speaks much more than points difference. Points said nothing. Alonso in 2008(5th)-2009(9th) , so all other guys who beat him then will be faster than him in the same car? Probably, but we don't know. Your question don't make any sense. Your point about inferior car has been overturn. Your question doesn't stand anymore.
No my Friend it's to do with using the evidence available to ascertain probability of performance. It's also subjective and personal. It also requires context, knowledge and experience as you have all pointed out.
MY OPINION is that
Narain Karthikeyan would have approximately f&&K all chance of matching Schumi in an MGP
Alonso, Vettel or Hamilton would have a high 90s chance of beating him in an MGP
Rosberg high 70s
Petrov, Heidfeld, Di Resta, Koba 60s
You will have your own numbers, I'm sure but I can guess what they look like.
What I take umbrage with is the response that a driver who is competing already with Schumi would have a chance of beating him rated at laughable. That is where this exchange has come from. If you take a deep breath you may see some common sense there.