Mutons/Berserkers fit more in my opinion.
Yes, yes, "wrist rockets" joke here, but B2s were designed to be heavy assault units, not artillery, and were deployed far earlier then people think, fitting the Mutons closer then the Mecs. And they literally had a model designed and fielded to face Jedi in melee with lightsaber resistant materials, making a point for the Berserkers. I can't think of what would fit for a Mec, but it wouldn't be a B2. Perhaps a Magnaguard with the launcher from the original Battlefront 2 to go as the mortar? Or there's a model I'm unaware of.

I mean you wanna play the deployed sooner card they were on the first battle of geonosis... Lets start having mutons mission 1.... I dont consider when in the lore they were prevalent as a very good deciding factor. I value what closely matches it just as the person who made the mod themselves wrote. Id argue they fit the mecs better, berserkers never had ranged and are already magna guards anyway which in my opinion? A better choice for that unit. To add, since it would likely get a mec jump, b2s could have a jetpack. Which can clear that part nicely. Mutons? Dont. Though if I had to pick something other then a mec id pick muton but as it stands I stay by my judgement.

Mutons show up in an earlier force Level then Mecs as-is, much to my annoyance in runs.
I never said Berserkers were ranged, and in fact, literally pointed out a B2 model that was solely built for melee for their replacement.
B2s *did* have a jetpack model, but generally any of the bipedal battle droids could have a jetpack attachment. It's a far easier modification to add to a chassis then it is to manufacture, deploy, and fit to armor as it was with the clones. Hell, we see B1s using them in space to cut open escape pods during the Malevolence arc.
Mecs seem too sturdy for B2s. They're stronger then the basic B1s, yes, but they aren't walking tanks.

Magnus have you played Republic Commando? Because in there B2s are Walking Tanks

If it's not already abandoned... how about a spider droid?