system
Given the following post, respond as if you're commenting on Reddit:
human
How does the terran compete with the zerg and protoss[SC2]

on a battle by battle and grand war?
gpt
(Gonna go more with lore seen in novels and cinematics than in-game)

For the most part, Terran firepower is MUCH longer ranged than either Zerg or Protoss. When the Protoss aren't glassing planets with huge capital ships, they tend to fight with Zealots, young warriors looking to gain glory and only a small handful of support units with advanced ranged weapons. But even that is a rarity for them. For the vast majority of the Protoss military forces (which may as well be their entire society, thanks to their near self-destruction during the aeon of strife and the ritualization of every aspect of their lives) they tend to sit and fight defensive battles rather than strike out. This often leads to them being overwhelmed by Zerg numbers or out-maneuvered by superior Terran tactics and range. 

While the zerg are EXTREMELY adaptable and are even more aggressive than the most bloodthirsty Terran general, they still tend to stick with hack-and-slash animal-like combat forms and only a tiny handful of support organisms capable of spitting acid or throwing spines. Neither of those biological weapons have any great range, either, so it's often child's play for a skilled Ghost or tank crew to destroy legions of zerg scuttling through a canyon or empty city before they can bring their claws to bear. 

To add to these points, while the zerg come close to human ingenuity and strategy, thanks to Sarah Kerrigan leading them, they still tend to fall back on ancient and proven tactics "swarm them with huge numbers". Very few human armies throughout history have employed the exact same tactics, or fell to them, more than once. Or they subtly changed their warfare strategies with every enemy they faced. That's humanity's greatest strength. We can change how we fight based on circumstances and necessity. Zerg and Protoss are too ingrained with their old and ritualistic methods of combat to see how often it fails them. 

But sadly, even these strengths don't always leave Terrans the victor. Even with perfect scouting, positioning, range and knowledge, bases will still run out of ammo and be overwhelmed. Or crafty Protoss will figure out gaps in security and slip in unnoticed, leaving everyone vulnerable to lightning strikes and eventually crushing force.