You are totally right there should be less ingredients or more potions.
I think that the problem of having more damage potions making the game too straightforward could be solved by making damage potions that need to be used smartly like potions that only works on walls, a potion that make the floor inflammed where you walked or a potion that push the monster touched making him deal damage to the monsters he enter in collision with. So that the player will need to think about good timings to use them and the position of the monsters, it would even make the "effect" potions more interesting because they would help you to put the monsters in positions where your damage potions are even more effective.
For the softlock part maybe the boss could drop some ingredient when you hit him and some ingredients could spawn around him (Like a worms boss which have horms getting out of the rock around him.) but the boss will need to be agressive in this phases so that the player can't exploit too much those drops.