e.g., Cianide seems bad, but it won't kill you if the relative volumes are small.
tl;dr: You haven't characterized the denominator.
> increase in a risk factor of over 300
Even with a numerator-only view, I suspect it's not fair to characterize the "risk factor" as going up 300x. There's a lot more nuance about orbits in space.
Getting back to the point:
You literally claimed that one of these would "inevitabl[y]" trigger a Kessler effect with no proof.
> something literally 1000x bigger be even more concerning.
Again, this isn't convincing if you don't have the denominator/context. Think about it: you still can't answer how many of these are needed to trigger the Kessler effect.
BTW, "increase by a FACTOR of about 300" != "increase in a RISK FACTOR of over 300"