So in Terminator 3, the evil robot must be even more hardcore terror-awesome than the T-1000, right? They wouldn't bother to waste our time with a sequel 12 years later without coming up with a cyborg so tit-shatteringly badass that the T-1000 would hang posters of it on its wall, right?
"I'm here to kill John C- why are you laughing?"
What we got instead was the T-X, a machine utterly inferior to the T-1000 in every conceivable way. Both could change their appearance and deliver menacingly deadpan compliments about peoples' vehicles, but while the T-1000 could shape shift into literally anything it touched of equal mass (even a goddamned patch of floor), the T-X was strictly limited to different variations of the same hot woman. There's even a scene where it inflates its human female breasts to more effectively coerce someone, and while we agree that this can be a useful ability, it maybe isn't as universally effective as being able to dopplegang virtually any person on the planet.
But that's not even the most severe design regression. The T-X, like Schwarzenegger's moldy old T-800, has a physical endoskeleton. If Skynet can make a time traveling assassination machine out of liquid metal, why would it ever build one out of anything else? The T-1000 could not be harmed by anything -- it shrugs off bullets, grenades and explosions without a scratch. Arnold takes the same abuse, but comes out looking like he got raped by a Tyrannosaurus, because he has a permanent solid-state structure. So why would a sentient supercomputer overlord read the performance reviews of those two models and decide "Whoops, scrap that 'mimetic polyalloy' bullshit, clunky metal horror-bones are definitely the way to go"?
Yeah, that's much, much better.