I would suggest an entirely different approach when it comes to damage, armour and penetration: raise the numbers

Hitting an unarmoured person with a solid projectile weapon in head, chest or groin is quite deadly. Almost always. Meaning a stub revolver should deal enough potential damage to kill an average Joe with TB 3 with a single shot!

A stub revolver with 1d10+10 damage? Why not?

On the other hand, modern armour should give adequate protection against primitive weapons. Like a stub revolver. For instance it should be virtually impossible for a stub revolver to penetrate Power Armour.

Power Armour AP 25? Why not?

When you are wearing power armour, it shouldn't really matter whether you have a TB of 3 or 5. Your body is made of bone and muscle, Power Armour is made of ceramite plates.

A melta gun is built to penetrate almost anything? Even Power Armour?

Melta Gun Pen 30. Why not?

I know that big number can get uncomfortable. But they can be fun, too! Don't be scared of them!

Because not all hits are square on with the target. Instead of claiming that the shot does hit the center of the head, perhaps the low damage nature of the hit is due to it grazing the cheeck.

Your proposed system fails to take into account some of the core mechanics of the game. It in no way accounts for how novice grade NPCs currently work. You could in theory deal an effect rank 57 wound to a novice, and, as long as its neither a critical wound, nor 2 separate wounds, it would not kill the NPC. Unless you're trying to propose a rewrite across multiple sections of the book, simply doing more damage isn't actually that good of a solution.

In this system, PCs are the fated few in the galaxy of the mad, who manage to get somewhere in the world. To this end they are exceptionally lucky, and quite often manage to not die, until that one shot finally does them in.

Who wants to play an RPG where their beloved character can easily be killed by a nameless mook with a Saturday Night Special...? Weapon damages are always scaled down from their real-life counterparts in RPGs, specifically to foster PC survivability.

That said, I do think the current (2Eb) values are too low- especially armour pen. I hope they get goosed up before 2E goes live- especially considering how much tougher cover is!