It occured me that all HP steal on hit / crit is a fixed amount or % of HP,  regardless of attack rate of weapon. This obviously favours faster attacking weapons / skills.  Other similar games have done it differently in a more "fair" way, eg Titan Quest (or Grim Dawn? or both maybe) which had something like "% attack damage converted to health".  The health return is proportional to the damage done. That means that if you have a fast attack doing small damage or a slow attack doing large damage, it works out you get a more even amount of health over time either way.