GE of the coronavirus doesn't make sense

According to the analysis of S&C, the accumulation of point mutations within the H1N1 virus occurred at 14,4 new mutations / year, which is close to what we saw this year for the coronavirus.

The number of accumulated mutations in one year is probably to small to have a clear visible effect on fitness. But if the coronavirus go on to accumulate ~ 20 mutations / year, I would bet that in 10 years, after having accumulated 200 mutations, a reduction in fitness will be seen.