sheen = enhanced autoattack and thus applies lifesteal
Bork is also onhit but the ability doesn't count as an enhanced autoattack.
But more to the point, the exception here isn't bloodrazor, bloodrazor is the normal one and is the poster child of all things lifesteal. It does exactly what its supposed to.
Blade of the ruined king is an unbalancable design that has just received special and unique case-by-case nerfs. There are a bunch of ways I could explain to you that it is justified that Bork does not proc lifesteal on the % damage but at the end of the day Bork is the odd man out.
You will find that the remainder of your conversations will make more sense under this logic
bloodrazor works perfectly
Bork is the weird one