I have great maneuverability in my siphoner leather armor and tabi boots.
At best it's "ok" maneuverability. Great maneuverability is when you have something like Hit and Run or Fancy Footwork, because that means that after getting close to the enemy and killing it, you can get behind the cover or run far away after. With only 4 AGI and tabi you have enough to get to the enemy, which means it's not that different from guy in heavy armor with Sprint. Good that you have dodge + evasion, but your agi is just too low for it to be the only defense you can rely on with 3 CON (and you didn't max evasion, that's bad, for melee it's more important than dodge, since most guys who try to get close to you will get killed quickly).
Also, 20 is definitely doable, I don't think Styg would put BH if you can't use it.
Also, if no - I always have usual hammers, not a big loss.
I never said you couldn't use it. I said you don't need to aim for 20. You can still use it without 20 STR, you just get accuracy penalty, 5% for each point you are lacking.
Look, the idea for this buld was to rely on stealth and dodge/evasion anyway, so I don't need Con.
The you should've probably put those points in AGI, since PER doesn't do anything for stealth and dodge/evasion. I too like to discover thing with PER, but it is not really useful even when using Oddity xp.
I already decided to give Pummel a try, but its usefulness is limited - I'm already using Taser, also drugs cot 10 AP which is a huge penalty compared to doctor's pouch users, so it could be useful if you really need to finish someone, which is rare thing at least on 16 lvl.
It's usefulness no more limited than that of taser. You can't use taser every turn, it has a cooldown, so you use taser one turn and pummel next. And if you are using setup that is different from tichrome hammer (like with Balor), then you still has those free 10 AP lying around, might as well put them to good use, like using pummel, taser or drugs.
So my pick is Nimble, Deflection, and some of these - Super Slam, Pummel, Clothier, Power Management, can only take 3 from 4.
Super Slam with 3 Con is really not that useful. Even on Easy it's less than 140 damage at lvl 25. Clothier is not that useful for your build, since you want to focus on stealth and evasion and the only fabric that won't push you armor penalty beyond 15% is black and aluminized cloth (blast having 15% penalty and kevlar is 10%), later is killing your stealth and former will get you less than 10 points in stealth (even with 160 quality cloth) from Clothier.
Deflection means that you'll have to keep one weapon slot open constantly and switching to it. If you aim for balor hammer i would recommend keeping it in one slot and tichrome hammer in other. If you need to use Balor, pump up on adrenaline and go to town, then if there is someone left standing, just switch to tichrome and finish them off, because when adrenaline expires it'll be harder to finish someone with just balor, due to accuracy decrease. And again, dodge is less useful for you then evasion, since there are less enemies who go in melee and they will go down first, most probably, since they will be closest to you.