As i already mentioned...
"Tenacity is garbage because you need huge amounts and after all you still get 15% RNG that you get a Debuff. Speed is also garbage because if he is lead by HK he will gain more than enough TM (even better with Counterattack)
In any Droids Team he is like an upgrade to IG100 and both have a lot of comparable stats.
Since his crit is lower than the DPS Droids he will need some support here to get him high enough under HK that nearly every Attack is a Crit. Next step is to get + crit damage and at least some more potency because you want his Offense Down and more important Daze. Rest is more or less Protection Upgrades since he is a Tank, will Taunt often and has high protection.
With JE his speed must only be high enough to start with all other Droids after that crits and Counterattack will ensure that he goes often enough even if he is debuffed. "
So you can go with Health Mods, Crit Damage or Crit. Chance it's all about the right mix because (under HK Lead) you wan't a) a Tank, which mean he must soak up some damage which should be more than Wiggs Opener! b) he must be at least fast enough to go first Turn after JE to avoid counterattack from TM Units like Biggs/Anakin etc. before he can taunt c) you need some +Crit Chance to fill TM with "Counterattack-Crit, go again" (= make his lower damage stack, same turn-loop as IG100 or B2) d) you need some Potency for Daze/Offense Down
My K-2SO currently is 7*, 85, Gear IX with full Omega Abilities:
around 49k HP/Prot (3x Prot. Primary)
Speed 162
Crit.Dam 180%
Potency 41% (need to go up higher)
Crit Chance 31% (+HK Lead, which means enough to start the TM Train)
So with more gear and some mod adjustments i aim to upgrade his damage (we talked about to cut IG86 and K2s damage grow slowly - i expect at least Gear X is needed) and Potency (at least around 50%) - Speed and HP/Prot. works fine so far, the latter one will jump with the next Gear level.