Make Sprite-Diffuse shader work on mesh renderer?

So, I'm working on a sprite-based game where I use the sprite-diffuse shader on most game objects with sprite renderers, to make them able to be affected by lights. That works great. However, I'm also using a mesh renderer on some of the sprites because they are being deformed in-game. Now if I'm using the same standard Sprite-Diffuse shader on one of those object, the lighting changes drastically. It is being lit, but much much weaker than the objects using sprite renderer.

Anybody got a clue where to start looking into t$$anonymous$$s? Found a few people with the same issue online, but no solution. Anybody know if a Sprite-Diffuse like shader exists somewhere that would behave the same on MeshRenderers?