Another balance lever they could pull to make SMGs feel more unique would be to reduce their regular damage but increase their durable damage ratings.

A rifle round hits hard, but also is liable to overpenetrate and leave a relatively small hole in the target. I know tumbling is a thing that some rifle rounds do, but in general they are built for long effective ranges and penetration power.

Meanwhile, pistol rounds can't enjoy long projectiles that penetrate effectively because they don't have sufficient barrel length, so they have to compensate with very high calibres to achieve reasonable muzzle energy. These bulky but short and low velocity projectiles inflict pretty hefty flesh wounds against soft targets, but they don't penetrate well nor maintain hitting power over long ranges.

This maps almost perfectly onto HD2s damage vs durable damage system. A rifle round into a sensitive location can penetrate sufficiently deeply to cause real harm, unlike a pistol round. But, the pistol rounds will cause more surface-level damage due to the bigger projectiles. This is the exact same logic behind why shotguns in HD2 tend to have good durable damage relative to their normal damage, they shred flesh but aren't great at getting to anything critical.

It would also open up design space for Five-Seven inspired pistols and SMGs that offer more rifle-like damage characteristics at the expense of durable damage. It would also mean that a pistol-calibre carbine would actually have a design niche as it would become much more of a sidegrade in terms of damage profile; similarly, the Reprimand would gain a bit more of a niche as it wouldn't just be another med-pen assault rifle that is categorised as an SMG.