I'm not the guy you responded to, but Bisping being champ paints a very, very, very flattering picture of how good he recently was relative to his competitors.
He got the title shot against Luke Rockhold because Rockhold's original opponent pulled out at very short notice, and Bisping was the only guy with a reasonably high ranking who was available. At this point, he was still regarded as a "B - level" fighter. Very good, but a step below the best.
He KO'd Rockhold in the first round. Fair play to him. It should be noted that Rockhold fought in an absolutely stupid way, having his hands down for the majority of the fight, which made it far easier for Bisping to clip him, and it was widely acknowledged after the fight that Rockhold is the superior fighter. I still would argue he was a B - level fighter then, if you define "B - level" to be a similar level of relative skill to the rest of the division as he was 5 years ago. He just had everything unfold perfectly for him, and he took his opportunity. A fantastic achievement, but we all knew he wasn't the number one in the division, despite having the belt.
After he got the belt, he was given a defence against the 46 - year old, number 13 ranked, Dan Henderson. Henderson had no mobility at that point, and relied solely on his huge punch. Bisping was given that defence as it was a "grudge match", and was seen as likely to sell well (which it didn't, actually). He was beaten up for two rounds, nearly KO'd, and won a narrow decision without ever having Henderson in danger. OK, he won, but hardly a performance you'd associate with the elite of the division.
Bisping then stalled the division for months on end, avoiding a fight with Yoel Romero, a true elite of the division, and the obvious favorite should the fight have ever happened. He instead took a fight against GSP, an all - time great, but from the weight class below. That's a big deal going from Welterweight to Middleweight, the size difference is vast, so Bisping had a big advantage in size. This was despite the fact GSP aggravated his dormant ulcerative colitis in trying to pack on size - it was clearly not his natural weight class.
Bisping got dominated. There's no shame in that, it's GSP. But it evidences he was not much better a fighter than in the era you were alluding to.
Bisping then took a fight against Gastelum, and was knocked out.
Although Bisping was a champ, that reign was seen as something of a joke. It seems to have become a lost narrative now, but that's how it was seen. I don't contest that USADA is catching a lot of athletes, nor that Bisping seems likely to be clean, but him being the champ did not imply he was better than his competitors, as paradoxical as that sounds.