What you are saying is simply not true. mRNA vaccines took absolutely no time to design, as they have an automated platform to synthesize any given mRNA. Companies have even disclosed they went from sequence to vaccine in just 24 hours.

Your point only applies to those with a recombinant vector. But even on those, Oxford were so fast because they already had a developed platform and they were working on a very similar epitope.

Spending a bit more time would have been surely safer, and would not have delayed things significantly. What we have now might not be good enough after all, if it's true that the SA variant escapes immune recognition on individuals vaccined with Oxford-AZ. I hope to be wrong.