No, it's certainly not a fact. They haven't even been the undoubted "best" club in Spain for decades now. The only fact is that they are the "biggest" and/or most-winning club in the history of the sport, which is no mean feat (although the fact that the first few "European cups" are officially recognised as proper CL titles is and will always be a joke). But claims like the ones made in the title of this thread are 100% subjective and 99,99% embarrassing in a fecking Manchester United forum. Madrid is a city which many people who truly know it, like myself, really dislike, the club has as much dirt and corruption as any, and the fandom can be as toxic as any.
This corruption thing is BS. You realize when we were successful in England, our rivals used to say exactly the same things about us, right? That we are corrupted and winning by the help of corrupted ref and fixed FA.. Etc. No one forgers the embarrassing "facts" presser Benitez made on us. Any losers in sport will say the same about the winners and it's always bollocks.
The toxic fanbase thing is subjective. As I said in another reply, it's easy to comment on other fans as toxic while labeling your own fans base great because you are part of that fan base. There's nothing indicating that we don't have our own toxicity, and honestly, pretty much all fan bases will have their decent side and toxic one.
Finally, they don't need to win the league and CL every year to prove that they are the best. Being so competitive almost every season in major trophies even when they are passing through shit periods or rebuilding the team is something many other clubs are incapable to do. They have 4 CL titles in the last decade alone which is the same number other clubs achieved (or even less) in their entire history.
I don't see the embarrassing part about the thread. Madrid isn't a rival, and just because I support United, I don't have to follow the propaganda and say we are the biggest club in the world and have the best ever fans. No one supports a club because it's the biggest club in the world otherwise everyone would have supported other clubs, so supporting other club and admitting that other club is simply better in every way is objective and realistic vision, no embarrassment about that at all.