This fails to consider if the vaccine is less effective you have faster natural infection that increases herd immunity per period of time. The R0 at 2 in a fully susceptible population if you remember from the original article says if the R0 was 2 as everyone said, the entire world would be infected within 32 weeks which didn't happen. The R0 therefore can't be a 3 and having a new variant more virulent than the R0 of 2 is immaterial to the spread.