I think part of the reason is because many of us (younger folks - ehm, although I'm 32!) grew up with Schumacher and were able to watch him live, while we were unfortunate not to have been able to watch Senna. With Schumacher, I also suspect the sport grew and was more widely broadcast, so his moves were a big deal. Senna, we just remember as being perhaps the greatest ever and of course his tragic death. Perhaps it is that, that makes us look at him under a different light.
I have no opinion either way to be honest. Perhaps the relevant question is; who did which moves against which drivers? A cheat is a cheat, a bold move a bold move, but if you are playing dirty against others who are doing the same, it perhaps is a bit different than if a driver is doing against other that are not. (Not saying it was this way - I really have no way to know and I admittedly never watched the Senna seasons to see his moves in proper context).
An example: On race 1, driver A might be very ruthless against driver B. Then on race 2, the whole thing escelates when driver B returns the favour and perhaps goes over the limit. That is putting it into context somewhat. From what I gather, it seems Schumacher didn't need to do what he did, which is why it's a big deal. Senna - I have no idea. He was as ruthless as a driver can be, but perhaps he was at least consistent in how he did it?
As for Grosjean/Verstappen; I think telemetry shows that Grosjean clearly didn't brake-test, but he was struggling with grip in that stage of the race. As an observer, I wasn't surprised to see the crash unfold eventually.