1)Equipment that adds to melee and ranged have other bonuses, as Kinak has stated that melee and ranged are the "primary" attack types, and the others are intended as flavor. Fire Power generally brings nothing more than a penalty to Fire Defense, and Etheric will often have a penalty to Will. However, if you look at the gear that gives the best stealth power, it actually rather consistently provides modest levels of power or defense to something.
2) It's actually not particularly hard to develop a 4 or 5 technique chain that's effective, given that, with a difference of 10 between best offense and best defense, even an attack that is power 4 is at least 14 damage. For example:
Assuming that the attacker has max +stealth power (+21) and the defender has max stealth defense (+11) with all other stats equal, stating MINIMUM possible damage:
(6) Dirty Trick: 8 base damage as opener +10 stealth): 18
(5) Fuming Acid: 8 base damage (assuming the defender's opener isn't ranged or melee) +10 stealth: 18
(4) Dirty Pool: 3 base damage +10 stealth: 13
(3) Acid Splash: 6 base damage +10 Stealth: 16
With that 4 technique chain, you do 65 damage, with 36 of it in the first two hits, only using stealth. If you want, you can add on a switchblade for a an additional 3+10 damage to bump the total to 78.
Even without the switchblade, if you have:
16 Will & Str, you're dead after two attacks.
29 Will & Str, you're dead after three attacks.
Strength and Will of 45, you're dead in the first round.
This is assuming an attacker that has NO extra damage from stats at all. If they've finished the current content, gotten a few more skills, or just leveled more than you, the situation is worse.
Really, what it means is that unless you can kill your stealthy opponent in one attack, you're probably dead.
3) It's possible that there is a wave of Stealth Defense gear out there that will balance it out that we haven't been able to find, and I can appreciate not wanting to add more obvious items to balance it for now when the situation will change once we discover more. However, for now I think PvP is, if not broken, at least unbalanced by this particular issue.