Mm, Nashoba, I kind of see where you come from... but if weapon variety is your primary concern and that you believe it's tied to damage values - then the possible 13 variations we have presently (from PDR1 to SDR5) is also pretty restrained.
In a way, perhaps I could work up an equivalency: PDR1~5 is anti-personnel, anti-armor is ADR2~3, anti-mecha ADR4~5, anti-starship SDR2~3 and anti-capital ship SDR4~5. The numbers felt crude, though, because we could be more evocative while granting more spotlight/credence to each role.
If we take a good look at the damage values we have now, PDR is for the most part useless, because we usually ignore it/rarely use it. People don't exactly have hit points, weapon lethality is a little hard to gauge when anything well placed could kill someone too (how much does a bullet hurt? How much does a sword hurt?), so, the real demarcation that appears to be noticeable is whether your weapon will, or will not, harm a power armor (PDR 1 through 4, or PDR5).
So, right now, it's not 13 variations and more like 9. We're not that far away from my proposed 5 damage roles here.
Given how the very widespread Star Army Nekovalkyrja Service Pistol is, handheld weapons that can harm power armors are actually rather common. This looks to me like it reinforces the 'can harm power armors or cannot' split, and brings home the fact that while a power armor probably can shrug off anti-personnel fire... it probably can't afford ignoring it (maybe even the less potent one - even Robocop couldn't shrug off continuous firearm pounding from an entire police force without being chewed off and staggering in retreat).
So, what we get here is the Anti-Personnel role. Where some weapons obviously won't be viable against power armor, and some might be. Personally, I thought common sense and weapon description kind of implied the distinction without anything more.
Was a category for the more crummy weapons truly needed? Or a qualificative (standard Anti-Personnel? heavy Anti-Personnel? Eww...) It looks to me like most of the special effects granted by smallarms would be due to their ammunition rather than their actual lethality. Armor-Piercing-type ordonnance could be that which might cause some harm, while incendiary could stop regeneration (on both neko and mishhu) and so forth.
But then, that's still within the bounds of just the anti-personnel role. Another thing could simply be weapon type. We take the simple firearm as the benchmark, but there's also the machinegun which sprays a single target with metal hail, or might inaccurately hose down several. A shotgun spread of pellets can prove devastating up close, and perhaps have the kinetic push to inconvenience a power armor. A sniper rifle ability to line up careful shot could count for something if a shot could be made against the relatively yielding neck section of a power armor, or to get at some other tender spot.
A M6 Daisy's forearm pulse cannon could also count as an anti-personnel weapon, since it's supposed to mimic the NSP. It's made to mow down anti-personnel targets, but can be of some limited usage against power armor.
The usual grenade as we know it would appear more like an anti-personnel weapon than anti-armor, as I bet you'd usually throw it to get at a bunch of people. However, it appears feasible to believe it might inconvenience a power armor. A bazooka/rocket launcher is probably not an anti-personnel weapon, though, since you'd usually think of bringing this up to shoot at a tank or an helicopter rather than shoot it on people.
*headscratch*
So, taking a step back, most of what I discussed still seem like weapons made to kill people, but some under that umbrella - under the right applications - could prove damaging to the tier above them. Those applications seems squarely based on the actual nature of the weapon itself... which appears centered on its descriptive text.
So... what's missing here? It seems to work out, offer plenty of variety within a damage range via the expected role of the weapon, and there's plenty of apparent room for everyone of those weapons to feel different. The damage tiers for anti-armor and anti-mecha pretty much are the big brothers of anti-personnel so if the problems can be ironed out at the bottom, we might be able to go from there.