> But that could change or are you asserting it won't
How can you interpret what I wrote to say that a new virus or variant certainly won't cause a higher fatality rate? Anything can happen at any time. For all we know, a new virus could become prevalent. Typically though, we base public policy based on things that have already happened and the likelihood of future things.
There is little reason to believe COVID will evolve into something more deadly. In general viruses rarely make this evolutionary step. Pathogens do not gain reproductive advantage by killing their host. This is why zoonotic pathogens are so dangerous ... when such a pathogen crosses over, they can go from causing no damage to their original host (bats) to becoming very deadly in the context of a human body. Indeed, if history is any guide, endemic human viruses eventually evolve to be mild infections or beneficial (there are theories that placental development is due to the presence and integration of ancient viruses in mammalian DNA).
Given that, unlike the flu which has natural reservoirs in birds and crosses over very frequently to humans, COVID does not seem to be bouncing between animal hosts, it is highly unlikely based on every understanding I have of pathogenic evolution that the virus will become more deadly. Indeed, delta variant, while more infectious (as to be expected) is not as deadly.
> . It doesn't claim 35% fatality, it cites the 35% fatality of MERS, a distantly related coronavirus
Except, MERS and SARS-Cov1 are zoonotic viruses, whereas the COVID variants are human evolved and thus unlikely to become more pathogenic. Zoonotic viruses evolve to be less deadly in their hosts. The zoonotic crossover is a chance event and given the viruses were evolved to not kill bats, they had not been exposed to any selective pressure to not kill humans. Now they are exposed to that pressure so we will see the fruits of that selection.
Also, as you point out, MERS is only distantly related. If this pandemic were MERS with a higher infection rate, then it would have been more concerning to begin with, but of course then it would also have evolved faster to be less pathogenic because the selection pressure would be stronger. But it's not. Even the earliest estimates (again, with assuredly bad data) were a fatality rate of 7-8%. They've gone drastically down, by orders of magnitude, and the new variants will continue to drop that.
It is good new variants are being created. The higher infection rate + lower death rate will lead to quicker herd immunity against a broader spectra of Sars-COV2 family viruses.