Have you considered changing the percent lifesteal to a flat health gain (that could scale with champion's level)? Because BorK just seems like a way to help AD champions who will build high amounts of Attack Damage and crit eventually rather than the bruisers who do not have the luxury or gold to spend on AD/Crit/ArPen/Lifesteal/Attack speed and defense.
Cerbearus2 votesOn-hit health gets pretty ridiculous man. (see: pre-nerf 
)
Samflash31 votesBut it can be controlled (see Pre rework 
)
ProfDrDeath1 votesNo, it cannot be controlled. At least not on a completed item.
The beauty of Lifesteal is how it scales with a whole host of stats: The user's offensive ones (AD, Crit, AS), as well as both the enemy's and the user's resistances.
HP on-hit only scales with your own AS and tankiness.
Cerbearus2 votesTBH it really isn't built for bruisers. As you stated, lifesteal works better with ADCs. The whole reason it exists is as an alternative to BT as a lifesteal item for ADCs.
A bruiser would build it is because it adds CC to often CC-less kits and adds a good amount of damage without having to stack it with anything, meaning you can build just one offensive item. Bruisers are often very good duelists, and BoRK is the ultimate dueling item.