The problem is that Johnson and his mob have wrapped everything about the project in the Union flag so it's tantamount to treason to say they've messed up in anyway, and a diplomatic incident if any other government expresses reservations about them. As
@Neiler says, the vaccine development done by the Oxford team has been fantastic, but AZs job in the partnership has been to help with trials, get it licensed, and manufacture it at scale. You could make a reasonable argument for all three aspects having encountered major issues.
People have been critical because the trials didn't have suitable participants, whether Americans for the Americans or the elderly for the Europeans. That rests with AZ. They hadn't submitted an application to the EMA until the new year, and to America until January. That was after both the Pfizer and Moderna vaccines. Again, that's down to AZ.
Lastly, despite receiving several hundred million Euros to build a manufacturing capability in Europe, they've clearly failed to do so adequately. We can't say that's down to their altruism with the vaccine because the capacity building has pretty much been bankrolled by the EU in Europe and by the UK government here. It's their job to use their expertise in drug manufacturing to do so smoothly, and it's been anything but.
I quite agree with you btw about it being shameful that Pfizer and Moderna aren't working with COVAX to ensure the whole world gets vaccinated, and it is wrong for them to be profiting from what is a global crisis. No doubts about that from me. We can be critical of them for that while also being critical of AZ for failing in other aspects, surely?