Are Recon Buggy rushes the end-all-be-all?
I don't really have a multiplayer mindset so I may well be missing something obvious, but while buggies are great on paper they do have some limitations in practice:
a) When it comes to operating outside friendly territory, logistics (of course).
b) Buggies don't really have effective options when it comes to OHQ usage. As far as I know there aren't any buggy-centric (or even buggy-at-all?) OHQ formations, which means at the most having your 2 integrated-independent detachments for every OHQ. But even then OHQ bonuses only apply in a relatively close distance to the commander, so it'd have to be a (likely expensive) mobile formation to begin with.
Why is OHQ so important? Not only can postures make a big difference, but the overall OHQ skills can yield
multiple times the effective strength (e.g. +300%!) for units under them. This isn't something you'll notice against non-aligned forces and minors since they don't have commanders, but non-integrated independent groups do seem to falter against an OHQ formation with a decent commander.
At least for caliber, I've noticed the higher caliber guns weigh more, and use more ammo per firepower compared to lower caliber, but cost less per firepower. That and there's a massive exponential decrease to attack power when you're attacking with a caliber of weapon below that of what the armor you're attacking has.
e.g. if an RPG and a infantry with a rifle had the same hard attack damage, the RPG would have much higher chance of killing a tank, because it has a higher "caliber"
For some detail on this, see page 322 of the manual. Generic small arms count as 20mm, which means 25mm armor has further advantages than just the health numbers compared to minimal 5mm.
(Also note that combat armor counts as 40mm, meaning it gets a pretty major boost against small arms compared to padded armor.)