Nice theory/ but black holes do not only exist because of collapsing super nova, which are only a very small percentage of all stars. They existed already before that, although some new ones are created.
All in all black holes do not keep growing in size, because of course they do not keep eating matter which is not in their proximity. Neither do they shrink because of Hawking radiation.
The presumption that some particles will not completely fall into the black hole has no underlying logic for it. Its mass will never be big enough or fast enough to escape the black hole. What is left is photons of light without mass, that do not contribute to the energy of the black hole, nor subtract it.
If apart from that there is radiation observed “leaving" the black hole, this is a constant difference; like the admosphere of a planet is not subtracting its mass; and not an amount if energy leaving its mass. Like a wave is a constant difference/ and not necessarily a loss of energy.