To me, a balanced game means that each race is equally viable at each stage of the game (beginning, middle, and end). But late-game we are so underwhelming. Both Zerg and Protoss are so strong late game.
Both zerg and toss have very scary late-game compositions. Zerg can get ultralisks, infestors, and brood lords. Toss has many deathball compositions, like skytoss (e.g., mass tempests for instance).
Terran has no such late-game composition. Specifically, our late-game damage is very weak. We don’t have that “deathball” composition that can win games like Z and P do.
Unless we win it in the middle game, it’s pretty much over. That just does not seem balanced to me.