The transmissibility/virulence trade-off does intuitively make a lot of sense... the more deadly a thing is, the less likely an infected person is to pass it on to others. If someone is incapacitated with Ebola, they're very obviously sick and precautions are taken around them. Compare with someone with mild Covid coughing and sneezing it out around the community.

It seems reasonable, but from the latest meta-analysis I've found, I don't think the evidence is yet conclusive.