bomb range up is necessary if you want a shot at beating long-ranged shooters like the Gals, and ink saver sub is great too. damage up is also good, since it can reduce number of attacks needed to kill after hitting with a bomb.
Hmm... I see. Here what I think - Since we can only maximize up to
6 different main abilities. I believe the six should include these:
Damage Up - As stated, have Damage Up reduce the number of hits for kill after a bomb. One Damage Up will make you do 1 Direct Bomb hit and 1 shot from your gun for a splat. Stack it if you are facing multiple Defense Up users.
Ink Recovery Up - I personally find this pretty important. Since you will be using bombs and your gun in sequence, you going to need your ink up if you going on the offensive or defending a zone.
Bomb Range Up - Since Bomb usage is essentially for this build you need that range to catch those in the 3.3 Range group (Gal, Dual, Pro). Remember to Jump to boost your throw even further.
Ink Saver (Main) - This is just me but I drained my ink a lot. This is your extra 2 seconds to last in a firefight without to retreat to recover your ink. However, Ink Recovery Rate Up is more valuable.
Run Speed Up - More movement speed while shooting or throwing a bomb is always good. Makes you nimble against your opponents. Help you close the gap against guns that out range you and distance yourself from guns with shorter range while shooting
Swim Speed Up - Get to places faster, Escape quicker, Close the gap sooner and Trick your opponent with your swift movement.
Ink Resistance - I always found this ability really important. The ability to withstand your opponent's ink long enough to walk/swim in it, reduce ink damage and Jump freely is a huge plus.
I am sure there is more but this what I believe are the main skills. Tenacity is good but I think that is more of our Twin Brother skills for Inkzooka than us. We are also not very Special Weapon reliant as the other weapons especially the popular one so the Special Weapon Ability are sort of useless. I believe Ink Saver (Sub) is a wasted ability. You need 3 Main abilities to throw 5 bombs with a full ink tank. You can already toss 4 without a single one.
Stealth Jump and Swim are preference with Stealth Swim being preferable imo. I don't Squid Jump :p.
Alright... what do you guys think? Shoot down my theory and help our brethren reign using Default Splattershot.