A spider ball python (with a spider gene paired to a normal gene) mated to a non-spider ball python is expected to produce 50% spider with wobble and 50% non-spider without wobble. That's not watering down, it's just statistics.
What is a spider x spider?
Is it a spider with two spider genes in the gene pair? If so, then mating it to a normal will produce 100% spider babies (snakes with a spider gene paired with a normal gene).
Or is spider x spider the mating of a spider ball python to a spider ball python (each with a spider gene paired with a normal gene)? Doing a Punnett square for this mating gives the following expected results:
25% normal (with 2 normal genes) -- alive
50% spider with wobble (with a spider gene paired with a normal gene) -- alive
25% appearance unknown, AKA super spider (with a gene pair containing 2 spider genes) -- possibly dead
IMO, when Kevin says spider x spider is fine, he means the second -- spider ball python mated to spider ball python. And it is fine because most of the expected babies hatch out, and those babies are just as healthy as babies from a spider ball python (with one spider gene) mated to a normal.