system
Given the following post, respond as if you're commenting on Reddit:
human
[Half-Life] Why are Vortigaunts so Badass?

So I was there at Black Mesa, where I first saw Vortigaunts. They were scary, but they weren't too *terribly* tough to put down. A few rounds from the 9mm could do it. But now that I'm working with the resistance, I'm seeing Vortigaunts all of the time. And they are immeasurably badass! I saw one take on like, a dozen antlions at the same time! The same antlions that I saw could basically tear a man in half. 

Not that I'm complaining. If they were as tough as they were back in Black Mesa, I probably wouldn't have survived. And if they weren't as tough as they are now, I would also probably be dead! So what gives?
gpt
Being enslaved undoubtedly didn't do them any good. Those green restraint things the Nihilanth (and later Combine) gave them likely cut or weaken their connection to the Vortessence, which gives them most of their ability. Having no connection to the dimension or spiritual plane where their souls exist reduces them to an almost drone-like state. Those green shackles are the Vortigaunt equivalent of a lobotomy.