Pros:
Leopard 2 has absurdly strong armor and the strongest sabot (second only to the Obj 292).
Abrams is fast, has fast reload, has fast turret traverse, and a proxy shell.
T-80 is as fast as Abrams, has great armor and good survivability, has small silhouette, has autoloader, and additional shell types (HE and ATGM)
Cons:
Leopard 2 is a bit slower than Abrams and T-80 (not by a large margin).
Abrams has bad armor and TERRIBLE survivability, big silhouette, very loud and very distinct engine sound, and is all around quite buggy.
T-80 has slow reverse (8 mph), 5° of gun depression, long reload, and a slow turret traverse (it’s not slow it’s just slower than others).
Spoiler
I’m not mentioning things like one less crewmate in T-80 cause that’s already baked in to survivability, or things like not being able to shoot backwards on Leo and Abrams cause it doesn’t make much difference.
In a vacuum, the Leopard 2 is easily the strongest with the T-80 close behind, and the Abrams in third only cause it can’t go lower.
The Abrams will be disabled or destroyed if shot by any sabot from almost any angle. The abhorrent modelling of the armor and internals mean you’re just one giant weak spot. The only advantage is speed.
The T-80 has pretty small weak spots, and they’re easy to hide. It’s also just a small tank in general, and it has large HE shells and ATGMs which are nice to have on hand. The real kicker though is that its mobility is near identical to the Abrams. If you recall, mobility is the only thing good on the Abrams.
I don’t think the Leo needs much explaining. Best sabot and best armor with a small mobility loss is a really great deal.
Warthunder, however, is not in a vacuum. The Abrams is backed by the strongest CAS in the game . . . or at least it used to be until planes like the Typhoon and Su-34 got added. Now America’s CAS is average, and has the worst SPAA outta almost any nation. The AH-64E is also kinda doodoo.
Germany and Russia are both back by strong SPAA and strong CAS. Germany has the better SPAA, and Russia has the better planes and helis.