At worst, the capabilities CRISPR and other techniques from synthetic biology give to genuine researchers will offset any mischief a hobbyist can do.
[1] This is no a frivolous statistical argument. It helps establish a lower threshold and when other factors are considered the effect is strictly increased. The are some counter reasons, they help to think about he problem, but they are less convincing.
Evolution solves these things by brute force, but only if there is an evolutionary pressure. "Pandemicity" is at best an accident, from an evolutionary standpoint, and so is lethality. Both happening at once, thus, is very hard.
An engineer could arrive at a solution faster, given that he knows the steps. But knowing which steps to take is actually the hardest part of synthetic biology.