He'll definitely have beaten better competition than Anderson did, that's for sure. Anderson's wins may have looked the prettiest but Rockhold, Weidman, Jacare, Romero, etc, are far better opponents than anybody Anderson ever beat during his reign.
Bisping won't be able to defend against all of those guys though, he'll lose to one of them, but if he did somehow manage to beat all of them, then he's definitely up there. It's far tougher competition than what Anderson had to deal with and almost everybody will say Bisping isn't one of the GOAT MW's or possibly the GOAT MW, but beating that kind of competition, including a win over Anderson himself (prime or not), Bisping arguably would be the MW GOAT then.
The competition of today compared to back in Silva's reign is a whole different level. The guys today are far better in every single way than the guys Silva defended against, that's a fact. If Bisping beat them impressively, the majority (probably everybody) will say Bisping isn't ahead of Anderson and I understand why, but I bet some people will be saying it simply because they just don't like Bisping, so they won't give him the respect/credit he deserves.
That's just how shit works with MMA fans. They don't want to give some fighters the credit they deserve because they don't like them. Some people don't want to admit how good a fighter really is sometimes, their hate blinds their judgement or whatever.
If Bisping can beat those guys, he definitely has a case of being the best MW ever. The competition today is leagues ahead of the guys Anderson faced, it's not even close.
I expect some people to shit on me for this post, but the truth is, Anderson had tons of favourable match ups and fought a lot of very one-dimensional guys who would get killed with ease by the top guys of today. The MW division today is full of killers, it's more stacked then it has ever been and if let's say Anderson was in his prime today, I honestly believe he would not be champion. The top guys are just way too good now, he would've lost to one of them, especially Jacare, Jacare is a HORRIBLE fight for Anderson Silva, stylistically. That fight likely would've never happened though because they're good friends and they train/trained together for a good while.
I'd love to see Bisping beat all of those guys and be ahead of Anderson. The competition isn't even fucking close. The only thing is that Anderson defended his title so many times, but against who? He only has a handful of GREAT wins, so many of them are really nothing special in terms of competition.
Rage on, Silva fans and Bisping haters.