That's not the point.

: I
: don't see it being called the "M41 SSR MAV/AW" Rocket Launcher.
: It doesn't break my personal immersion if there's different types of
: rocket launchers. In fact, it adds for me because it's unrealistic for
: there to only be like 10 guns in the ENTIRE Univerise of a world like
: this. Especially now that's its several years past 2552.

Except that you don't actually see that sort of weapon redundancy in real life. You see different weapons across different militaries and maybe different branches of the same military. It's been established that everyone in the UNSC uses the MAV/AW, from ODSTs to Marines to the Army. And an organization as large as the UNSC isn't going to drop a longstanding design for something that offers the same performance.

That's only half of the problem.

: I like visual consistency too, but I also like a world I can believe in. So I
: 100% accept new weapons, as long as its mentioned that they're different
: models or whatever if they're replacing something like an AR or Rocket
: Launcher.

The other problem is one of icons. These guns are iconic, they're a part of Halo. Furthermore, they have a weird design that sells the universe as a science fiction setting. So, if they're going to redesign the assault rifle (Replacing the MA5, not retconning it) it had better not look like an M16 derivative. If they're going to redesign the pistol, don't make it look like it came from the desk of John Moses Browning. And if they're redesigning the rocket launcher, the end product shouldn't look like a Carl Gustav.

Contrast the shotgun. They're free to redesign the shotgun. They have redesigned the shotgun. Nobody gives a flying fornication about the shotgun, because it's too generic for anyone to have developed an attachment to the design.