Hello,
Some answers:
Decal mask
If something is not available without Substrate, then it is expected for it to not also not work with Substrate. So this is independent from substrate and it is current engine status: decal mask is no longer available as reported by the error.
Light DrawCount
Thanks for reporting with repro, I will add a task to investigate what is going on with that counter. (substrate do not add any lights but it does do more passes for the different material complexity tiled on screen so it could be just that).
DBufferDecal
Substrate does require DBufferDecal for decals to work. (this is because the GBuffer is no longer blendable so decals are combined with substrate slabs/closures differently).