Well the quality of each tank, and numbers of units built show it pretty clearly. USSR held to having several tanks types in circulation, and even current generation having a "zomg good but expensive tank" and "looks like above but is cheaper to build".
By '80es Soviets did completely fall out of pace and by end of '80es latest versions of M1A1, Leo2, Chall2 and friends were quite better than anything Soviets had.
AFAIK T-80 factories were mostly in Ukraine so T-90 versions are all T-72 updates, and T-72 show its "quality" in Desert Storm (there is only as much as can be written off by "lolArabs&Tanks", to perform that catastrophically the basic design has to be crap and then some).
All the big myths about fields where Soviets had quality or supremacy are myths. Crap tanks, crap guns, crap metallurgy (because of utterly crap communist materials sciences and even worse quality control on everything), crap jet engines leading to crap jets no matter how good the geometry of design is.
They kept building tiny tanks because they never could build good enough engine, even those small light tanks were almost all underpowered. They defined their entire land doctrine around acknowledging that their tanks cant go against western tanks on anything near equal basis.
Now after all this pissing on all of it, I will say that Soviets had enough stuff that was "good enough", but technologically they were the underdog, scraping to catch up, for entire Cold War.
And in their rare lucid moments they were painfully aware off all this, and were honestly terrified of USA which could outproduce them while having superior quality on any field.
Russian hardware and doctrine were never as bad as Tom Clancy or Stuart Slade would describe them, but were honestly barely keeping in competition at best of times. Of course, even most cursory comparison of WarPac and NATO economies would explain everything and make it painfully obvious.
"OMG the Russians are out to get us" only existed as propaganda to support defense budget increases. Never since WWII had Soviets actually believed they could attack West and win, their only long term plan was "try to keep our act together until historical inevitability and internal contradictions crush capitalists".