Ah ok, I wasn't sure if you were on about the same thing.
My point is that there are alternatives in theory, but not in reality, as they're not already made, approved and waiting in abundance or being made rapidly, even AZ itself does not fit these criteria, so no other can and AZ will get there first. Having a potential alternative in the future is great (obviously better), but it's not the future yet, it's now and the risk is more now than it would be in the future. Delaying a dose so someone has to wait for 3,6,9 months longer is completely bonkers. All that time they could be catching and spreading, and each on missed is four more covid cases (which is certainly more risk).
I could see a point if we had equal measures of Pfizer/ AZ, but we don't, and won't. I'm certainly not an expert but I can't see why an AZ vaccine would be more risk to someone younger than it would be to someone older unless it can do more damage to younger, healthier and fitter people, but I can see how it would be harder to detect in older folk, as they're more at risk of everything, or there's more risk of something else killing them first (and the hypothetical clotting not appearing). Also, more older folk have had the Pfizer jab, as that is what arrived first.
The other vaccines (Moderna, Johnsson, Novovax etc) are incomparable also, as they've not had the same use, same setting, same virus, same timeframe, not approved at the same time etc. They could all end up a lot more risk than AZ, even Pfizer could if people did enough digging.
Just take whatever is ready, whatever comes first, anything trialled and approved is better than nothing, whilst the risk of catching and transmission is high, this would even be more reason in Europe or the other areas not doing so well, compared to the UK.