The current problem with life on hit is that it does not scale based on the hero's damage capacity. The raw, static number is the sole result of gear, and, due to the absence of pertinent gems, it becomes challenging to enhance it adequately. I understand there is also the basic regeneration, but its potential is completely overshadowed in a fight (I mean really, who relies on this stat?).

Given the diversity of gear setups one can go for, an increased vitality will require higher rates of life on hit - not because you will want to alleviate your OCD to keep your health bar constantly full, but because life on hit should scale with life.

How about a percentage of life on hit, which is also the common mechanic in most games out there? It could have a range between min. 0% - max. 60% of damage dealt on the enemy. This will also allow critical hits to restore a proportional, and reasonable amount of life.