A hybrid is simply two different alleles at a single locus.
A purebred is the same two alleles at the locus.
Dominance and recessive are two concepts you need to understand to know how evolution takes place. Your take on hybrids is somewhat overblown. And numbers of chromosomes are a big barrier to interbreeding. That is why some think that a change in chromosome number could lead to instant speciation.
OK, I'm backing out here, not being an expert. But by your definition every sexually reproducing individual is a hybrid.
I didn't say differing chromosome count is not a barrier. I said it is not an absolute barrier.