This is a key flaw in your logic. The choices aren't just "get the AZ vaccine" or "100% chance of catching COVID", so you need to multiply the IFR of COVID by the chance you'll catch it to have a fair comparison.
And even if the chance is only 1/4, I would estimate that the numbers would still be higher for covid than for AZ for people in their 30s and above.
That seems unlikely. For one thing, after more than a year, there have been 130 million cases out of a population of 8 billion, which is less than 2%. Do you expect this to dramatically spike in only a few months at this point? Also, remember that there are other vaccines available, so it's not the case that AZ or catching COVID are the only two ways to herd immunity.
I'm making the assumption that we want to reopen our economies again at some point, at which point the infection risk will obviously rise much higher than that (unless we have reached herd immunity). The only way to prevent that is to get people vaccinated. And right now for many countries in Europe AZ is the only vaccine available, since the supply of the mRNA vaccines is for too low.