This year we kill it: Corona Virus Thread Mark II

[Squire Doodad]

In particular, the "boosters aren't important" conclusion was because at the time, there weren't any signs of waning resistance, and getting vaccines to more people was more important than keeping up then-maintained antibody rates.
The actual conclusion is closer to "so far, antibodies have been holding up, so we're better off using spare doses on unvaccinated people than giving boosters."
Prioritizing unvaccinated people getting vaccines is still important, but now we're seeing signs of waning resistance in elderly groups 8 months in, so a booster is a good idea based on what we now know.
Said waning is not because of mutations but rather because antibodies don't always persist indefinitely. Once everything is under control, ensuring there's a long-lasting generalist vaccine can finish off the problem.

You could argue there's value in waiting because of this, but there's almost zero opportunity cost here. Besides, no one can see the future, scientists couldn't have known all this ahead of time.