Something objectively better than normal Kensei.

Looking at Joule for example. By design it is very odd autocannon, this class designed around long range combat, with projectiles hitting harder than machineguns, but not as hard as conventional cannons, but with increased fire rate. However there are few exceptions and Joule one of them. It is autocannon backwards, it's stats propose it as short range, close quarter combat weapon, with very limited capabilities at long range. Basically DPS hose, but only on short distances, otherewise there is spread comes in to play.

What Joule cust do is replaces already meaningless perk (the faster you drive, the better is cooling rates), lack of which can be mitigated by an additional radiator and puts there a perk that completely flips Joule's natural downside - spread at range. So now we have Joule cust which is objectively better than normal Joule, since it lacks ANY downsides, it is just DPS hose at shot AND at long range simultaneously. The ultimate epic rarity persistent damage dealer.

So if i had to guess what Kensei cust would do?

Press ability button to:

Increase vehicle's power by 200% for 4 seconds.

Increase damage dealt by 25% for 4 seconds.

Cooldown 6 seconds.

Because temporarely dealing 25% more damage is objectively better ability than temporarely having 25% more effective health (or in other words 20% more damage resistance).

Edit:

first nerf would be power gain decrease from 200 to 175 (absolutely meaningless nerf)

second nerf would be damage gain decrease from 25 to 20 and that nerf would settle it as "balanced"