Dear Janko,
Thank you for explaining, and for the references you give in the next comment. There are many unknowns here, and I think that neither of us can anticipate right now all of them. - We don't know yet the correct theory combining GR and QM. - If the radius of a black hole is known, its volume is undetermined, in the sense that it depends on the coordinates. - There are extremal black holes, which don't have a real event horizon. - The dimensional reduction which takes place in my approach doesn't imply with necessity the existence black holes lighter than the Plank mass. I just show how we can solve the problem of singularities, in GR. In the correct theory which unifies it with QM, things may be different. But since my approach provides a possible way to regularize quantum gravity, it may offer the answer (there is still much work to be done here). Anyway, quantum mechanics may add constraints to my theory, which are compatible with it as it is. For example, it may forbid, as you think, Schwarzschild black holes which are lighter than Plank mass. But this constraint is compatible with the theory. Now, I don't intend to give you a proof of compatibility. I consider your burden, to prove the incompatibility. Your statement seem to refer to GR in general, not just to my approach, so if you will prove this, it will be an interesting result. But my opinion is that there are more unknowns which are easily ignored.
Best regards,
Cristi