What level is the character you've given Leech? And how much HP etc? I mean those are small heals... but they add up to one decent or big heal over the course of many turns. Leech could be a bit stronger, though. Just a bit.
They're like level 4? I'm fairly certain with well over 100?
And the issue isn't even necessarily that the heal is small, I guess, so much as it's that the blood is EATEN by the walking through it. As in it is removed.