This reads to me more like assuming all terrorists are fundamentally incapable of anything remotely intelligent

The first paper you linked there lists 9 deaths and 806 injuries across 50 years. Conversely, you can look at a single example like the Manchester Arena bombing in 2017 and see deaths and more injuries from a single event using simple techniques where materials and instructions are readily available. It isn’t unreasonable to look at the lack of success of amateur biological and chemical attacks and assume that plausible future attackers will be intelligent enough to simply take the tried and tested approach.

On the other hand, there might be some mileage in hyping up the threat of diy countertop plagues in the hopes that would-be terrorists are as credulous as so many politicians and media figures are, and will take the pointlessly inconvenient and inefficient option which will likely fail and make life a little safer for the rest of us.