Warlord's Bloodlust; How to properly balance it

The wrong direction is make it proc on enemy champions only, as this will make the keystone never see the light of day. Since the exploit is on champions like Fiora, Yasuo, Tryndamere, and Gangplank who get early ways to proc it, not that it grants life steal from crit chance every 2 seconds since marksmen cannot get it until mid game at earliest then it needs to be fixed for champions do not get power from it until mid game, this nerfs the exploiters and has it the same power for the late game for the champions it is meant for.

Warlord's Bloodlust: Critical strikes heal for 0.6%(+0.8% per level) of the damage dealt and grant (+1.5% per level) bonus attack speed for 4 seconds (2 seconds cooldown). --> from Critical strikes heal for 15% of the damage dealt and grant 20% bonus attack speed for 4 seconds (2 seconds cooldown).

This solution will fix the exploit cases, but still make the mastery strong mid to late game like it is suppose to be strong in and for the champions it is meant for; it can of course still be used for the exploiters, but it will no longer be overpowered on them.