You just said it yourself: 400 hp isn't much if 2 or 3 people gang up on it.
That's the thing: even a battlesuit has trouble competing with a Tyrant. His Luci shots, while doing about the same amount to the Tyrant as a slash does to him, take seconds to charge while the Tyrant slashes away. Then, if you get a good shot in, the Tyrant charges away and your Luci shots can't keep up.
It SHOULDN'T take 2 or 3 guys to take down a Tyrant, not when they've got the best equipment. Now, I'm not saying the luci or bsuit is weak, and I'm not saying the Tyrant is super-strong either. I'm just saying that it's much easier to kill a bsuit+luci as a Tyrant then the human can kill it.
And no, it's not all balanced for the pros. That's why Dretches bite automatically, so that newer players stand a chance. It's little things that make it fun for newbies so that they WANT to learn, and balanced for all skill levels.
Instead of an hp nerf, maybe Tyrants could just have a half-second (or slightly shorter) windup for their slash? They'd still have the attack rate they do now, they'd just have to compensate for a small offset on their attack, which would inject a little skill into the slashing. They could even hold the trigger down to keep a swipe charged. Would that be a more acceptable way to balance them? I just think there's something wrong when it's much easier for Tyrants to kill bsuits than bsuits to kill Tyrants.
Also, looking back, that goon idea is pretty weak...

I take it back, s3 goons are fine how they are. The only unit balance issue I can see is the ease of Tyrant slashing