Honestly can't take people seriously who have Fedor as the GOAT. Resume to resume comparison, he simply doesn't match up to GSP, Anderson, Bones or Aldo.
Though I will say he's unquestionably the HW GOAT.
Here are some reasons:
1) Fedor is at HW where it's harder to not get KTFO
2) At HW you can give up bigger weight advantages e.g. Mark Hunt & Bigfoot are giants
3) He doesn't have good training camps or coaches like the other 3 so you could argue he has not performed to his full potential, he rarely gets to train with pros like the others, just rolls and spars amateurs
4) During PRIDE was literally seen as invincible, only AS has achieved this aura IMO JBJ has seemed beatable
5) He has several victories where he fought to his opponent's strengths and won e.g. grappling Nog, striking with Mirko (was actually kind of even), judo slamming and armbarring judo medalist Ogawa
6) Beat both former UFC champs Arlovski and Sylvia in less than one round
combined
7) Has
never been dropped standing despite over 10 years fighting at HW, only once grappling
8) Like AS, has "spectacular" looking victories
9) AS's resume is not much better, AS mostly fought
VERY favorable match-ups
10) Shown unbelievable feats of resilience such as surviving the Randleman death suplex
P.S. When he lost to BF and Henderson, in those fights I think he would have lost to ANYONE quite honestly, I really don't think he was in it at that point. Hendo was in PRIDE, it's hard to imagine if they had fought back in one of the PRIDE tourneys it would have gone the same way.
Those are just some I can think of.
Also you have to account for the era, JBJ is more recent. Probably if Fedor was just starting out now with Greg Jackson's camp and the most modern training and fighting knowledge he would be just as dominant as during PRIDE. In boxing rankings they account for era too as some of the guys who are ranked highly would be most likely beaten if they were to compete as they did in their prime in 2015.
JBJ might be the best but against guys like Gus who look more his size I think he has shown vulnerability plus his test results looked sus that one time (I use roids by the way). AS used peds. GSP APPARENTLY used HGH but I'm not sure about that, it's just a rumor I've heard a lot and those pics of him with "HGH gut".
FWIW Fedor looks a bit "sus" lately too but he has a big frame so it's hard to tell. I mean it's impossible to make accusations towards anyone who hasn't actually popped so we can only say AS for definite.