On the paper .44 my not be that fancy but when you take damage threshold, critical hits (Steadfast Aim) and special ammo into account they can easily outdamage the other pistol variants.
.44 isn't all that much better against armor since it has a ridiculous damage spread. It can either punch through easily or deal almost no damage at all, while 9mm will reliably punch through.
Steadyfast Aim is terrible since it requires 6STR and penalizes the use of rapid reloader. It's basically weaker Recklessness but the requirement is not worth it, it would be better to pump PER and take Sharpshooter, if anything.
.44 explosive deals 15-30 heat and 15-30 mechanical which is 30-60 total. Compared to 10-20 acid 9mm it might seem like a lot more, but 9mm gets far more shots per turn, not 3 times more, but all in all the benefit is negligible, and mechanical/heat is usually easier to resist (except for mutants).
And if you want to tak everything into account, .44 is even worse as it benefits less from Expertise due to it's low amount of shots, and is far less AP efficent so it benefits less from adrenaline/Blitz.
It's just bad, and especially bad on pistol builds. Tommy gun is fun though, basically a grenade launcher if you load it with explosive ammo.