It makes sense in universe that the Allied forces were able to gain the upper hand against the Soviets. While it appears the Allies are outmatched in tank technology, base defenses, infantry equipment, airforce, and so on, the Soviets have a lot of questionable experimental stuff that they strained their budget on. It would probably be little surprise that the war was won through robust Boring, but Practical solutions.
The Heavy Tanks are outmaneuvered and outnumbered by the Allied Light & Medium Tanks and are more expensive. The twin cannons don't help much against the agile Allied Tank divisions, while the Medium Tanks match the durability of the Soviet Heavy. In gameplay, this advantage is apparent when queued movements are used right after you order tanks to attack a target, enabling firing on the move.
Mammoth Tanks are very sluggish and expensive. The 120mm cannons and Tusk Missiles don't have amazing attack power, considering how slow and expensive these tanks are. Again, Allied tanks can out-number them 2 to 1 and easily out-maneuver them. Not only that, but the Tusk Missiles are very inadequate against the Allied Longbow Helicopter while the Helicopter's Hellfire Missiles will do good damage to the tanks.
The Soviet advanced infantry types are Awesome, but Impractical, like the Flame Soldiers and Shock Troopers, easily handled by anti-infantry vehicles or even basic Riflemen if necessary. The Allies went with the basics, with Field Medics and Mechanics to maintain wellness and longevity of infantry and vehicles respectfully, and used spies and professional thieves to level to playing field.
The Rocket Soldier is a far better secondary infantry unit compared to the Grenadier, as the latter cannot attack aircraft and dies in an explosion, damaging any nearby friends, even killing them. The Rocket Soldier is notably one of the few reliable anti-air units on the ground, which helped the Allies retaliate against Yaks, Migs, and Hinds.
The Soviets don't even have a proper navy to support their submarines, which gives the Allies an easy time moving naval support into position for the counter attack into Russia.
While Tesla Coils are very damaging, they are still static defenses and require power to operate for added total cost of purchase. The Flame Towers are also very limited in range and the slow fireball can be dodged by vehicles easily. The Allied Pillboxes are relatively inexpensive, use conventional machine guns and, in groups, can make a surprisingly good hindrance against vehicles, with proper army support. The Allies are less reliant on power for base defenses, only needing it for their anti-air machine guns, but Rocket Soldiers don't need power at all.
The Giant Ants campaign has a very specific unit lineup available to the player, comprised of a mix and match of Allies and Soviet units: on the Soviet side, the Grenadiers, the Mammoth Tank, and on the Allies side, the Ranger, the Medium Tank, the APC... Not only that, but your army is colored yellow... All of this adds up to one simple fact: you are not the Allies nor the Soviets. You are the Global Defense Initiative.
Or perhaps not GDI per se, but a predecessor organisation — GDI was only founded in 1995, but it was reformed from a UN-affiliated organisation that had already been active for some time by the late 80s.
The Allies make use of Anti-Armor landmines, created for the sake of stopping enemy vehicles and giving their footsoldiers a better fighting chance. The Soviets, on the other hand, use Anti-Personnel landmines, made for killing soldiers. It's perfectly in-character for the Soviets to make use of weapons that are now considered a war crime.
