I don't think we're meant to spam subs like that. It's generally a matter of toss sub, fire away for a little longer than you could without the sub efficiency. If gear can have double stacks of the same ability, maybe 6 stacks will net you a fifth sub toss, but... why?
The thing with gear is that a player should build for the map, their weapon, and their play style. If One is prone to dashing around in ink, they probably don't need ink efficiency or faster ink regeneration. Fast ink swim speed would be more their style, especially when wielding a primary not all that great in CQC-mid range combat. Faster ink regen and ink efficiency are more appropriate for all out offense styles that just don't stop inking. The Splattershot Jr. for example by default pretty much eats an entire tank just throwing a single splat bomb. A few of these sub efficiency bonuses will give an inkling room to throw a splat bomb and lay down some fire, but not much.
I have yet to properly gauge the effects of offense and defense ups. As far as I can tell, their effects are so marginal nothing really changes.
Some effects I'm not sure will ever be useful though, like ink resistance. Rare is the situation when someone would be marching through enemy ink for any length of time when they could just pop a few shots at their feet to solve the problem. At worst, their tank is dry and they're stranded in enemy ink, but then, that's a huge blunder experience can easily avoid.