1) the most contagious variants have emerged from countries with little to no vaccination: UK before vaccination and with very little protective measures (pubs, etc.), Brazil with Bolsonaro, India with a very high population density who are mostly unvaccinated, etc. These variants appear thanks to the high number of contaminations. Vaccination means fewer contaminations, and thus the less likely arising of mutations and a new variant.
2) Current vaccines are very effective against the current variants. This observation is inconsistent with the assumption that one of the variants could have been naturally selected to resist to vaccination. This is also expected as the percentage of vaccinated people is low in most parts of the world, thus there is little pressure to select a vaccine-resistant variant for now.
If we had made the variants "worse" because of imperfect vaccination, we would have seen a vaccine-resistant variant emerge from one of the vaccinated (>50%) countries.