I’m not bio-related or anything, but a popular theory is that what we’re seeing in data (where different strains can be observed to develop mutations at a particular spot) can be explained by convergent evolution, which can possibly mean that the variants are running out of new adaptations and converging into local maxima.
Relevant scientific american article | Relevant bioRxiv preprint
This won’t impact any major point of yours but a nit for this reasoning: law enforcement do sometimes pose as other law enforcement agencies to secure cooperation; a recent example in the US is ICE posing as local police.