system
Given the following post, respond as if you're commenting on Reddit:
human
[Terminator] [Spoilers] Are T-800s the strongest and durable Terminators? If so, then why

Didn't Legion continue mass producing it?

In the first movie, it survived an explosion, shedding its human skin and was only killed by machinery in a warehouse.

In the second movie, it loss an arm and kept on fighting the T-1000. It wanted to be terminated in a pit of lava, which was enough to kill him.

In Rise of the Machines, it was beheaded and kept on functioning. It was finally killed by using its own fuel cell, taking the T-X with him.

In Salvation, it was COATED IN LAVA and managed to keep on moving and nearly kill John Connor and Marcus Wright.

In Genisys, it survived in the time-travel machine and killed the T-3000. It was then combined with the liquid metal, essentially becoming a powerhouse version of the T-X.

In Dark Fate, the thorium reactor was enough to kill him as well as the Rev-9.

Why didn't Legion create their own versions of T-800s? Grace, a human with cybernetic implants, was able to dance around with the Rev-9. Marcus, the 'first' infiltrator prototype was able to powershove the shit out of the new T-800.
gpt
It's neither the strongest nor most durable, but it is the most efficient.

As an example, take the AK-47. Its functional design hasn't radically changed since well... 1947. Why are people still using it? Many, many more advanced rifle designs have been created since.

Well, it's simple, tough, versatile, inexpensive to mass produce, and it *works*.

Same with the T-800. It's durable  enough, strong enough and with its neural network, versatile enough to serve perfectly fine as a human-hunter. It doesn't require extremely advanced materials, and can be covered with flesh easily allowing time transport.

It's only with the advent of the ability of human targets to reprogram T-800 for defense in the past, and development of effective tactics to destroy T-800s in the future, that it becomes necessary to create advanced models.