First sentence is O.K., I would agree with that. However, the second part is more myth than reality. Soviet tanks were much smaller and lighter than average Western tanks. For example:
T-54/55 - 40.5 tons
T-62 - 41.5 tons
T-72 - 44.5 tons
And now Western tanks:
M48 - 52 tons
M60 - 60 tons
Leopard 1 - 42 tons
Chieftain - 55 tons
Challenger - 62 tons
As you can see, Soviet tanks were usually much lighter. (source: fas.org - numbers are a bit different than I remember, but let's believe them for now)
Well it really depends on what era you are talking about, in WWII they certainly did have the biggest tanks, especially early in the war.
SovietT-34 (1940) - 26 tons
KV-1 (1940) 45 tons
T-34-85 (1943) - 32 tons
IS-2 (1944) - 46 tons
USStuart (1941) - 15 tons
Sherman (1942) - 30 tons
Pershing (1945) - 42 tons
BritishMatilda II (1940) - 27 tons
Cromwell (1943) - 28 tons
Churchill (1942) - 38 tons
The Soviet & Western design theory changed radically after WWII, as the Soviets built large numbers of medium tanks, and accepted that there would be heavy casulties.
Meanwhile the west (with smaller numbers of tanks) built very heavy and expensive tanks, wanting the maximum survivability in each tank.
In the BT world you might have a Russian(Soviet style) army with large numbers of simple, cheap yet heavily armed & armoured tanks, while the invader might have a smaller number of better capable but costlier top of the line mechs.
If you´re basing them on the WW2 era, then no. The T-34 was cheap, rugged and plentiful, but technologically fairly primitive - they didn´t even have a radio in each tanks. Their purpose was to survive the weather, the poor road network and poor or no maintenance in the field, and then bury their opponent by weight of numbers.
Remember that the T-34 came out in early 1940
Compared to what Germany had in the begining of 1940 (mostly Pz II's) or the USA (no tanks at all) the T-34 & KV-1 were hardly primitive.
Consider the problems that the West had with tank/antitank guns vs the Soviets.
Right from 1941 the Soviets had the excellent F-34 (76mm) gun, which fired both AP & HE shells. (in both Zi-3 AT guns, T-34 & KV-1 tanks)
They also had the Zi-2 57mm AT gun, very effective vs German tanks in the first 12 - 18 months of the war.
In 1943 they introduced the 85mm gun for tanks
The US 75mm gun used on the Sherman had much weaker penetration, and was clearly out matched in an antitank role by 1943. The 90mm gun was much better, but didn't arrive until the last few months of 1944.
The US was still using the 37mm AT gun until 1943, and when it became clear that it wasn't capable of dealing with newer German tanks, the British designed 57mm was rushed into service
The British 6 pdr (57mm) was probably the best Western tank/AT gun in 1942, but early models lacked HE shells.
So it was really the "technologically advanced" Western Allies that were playing catch-up design compared to the Soviets