Their tech and engineering are solid. Their stuff is well-built and has been since the 1930s, its just roughly built.
US Tech and equipment are often cutting edge, and works well in service, especially carrier aviation and fleet stuff which Russia hasn’t focused on in a long time. But its expensive and probably irreplaceable, during a big war.
Those USSR designs and the tanks are old, and outmoded, but they’re plentiful and assad has lost some thousands of tanks and AFVs and still has thousands more.
The Russians are clear leaders today in reactive, kit based armor and active defenses–some of these sensors can detect the launch of a WGM (Wireguided missile) and slews the gun automatically down the flight path, firing in suppression against the AT team, before the missile can complete its flight (hopefully). There is a revolutionary (but simpler) system (that the US also deploys, but not necessarily on tanks) that fires an intercepting projectile against the approaching missile to destroy it right before it hits the vehicle.
These systems, if widely deployed, would eliminate the need for ever thicker armor, using better defenses, instead of layering on more of the same.