EU has had a supply bottle neck from day 1, you can easily see it in data:
vaccinetracker.ecdc.europa.eu
You have to take into consideration that EU only gets doses once a week (so numbers of real full use are only usable on tuesdays) and that EU countries might save part of the vaccination for second doses, so 80% use is still quite high.
The entire "EU is not using AZ" was basically taking bad data and presenting it with an excuse that was not the cause (the problem was logistics of AZ start up due to age gating). AZ use has ramped up since those articles, going from initial week 10% to now upwards of 50% in most big countries (which are the ones whose logistics took the longest to adapt to different vaccination teams), and numbers would be much higher if not for the temporary stop.
"Delaying the ordering of stock" is a bit of a stupid excuse when the contracts directly state that you are supposed to have the same level of preference as any other customer and you dont have anyone in front of you (which AZ lied about).
The motivation behind this is that AZ has delivered less than 30% of their original ordered Q1 (from 100M -> 30M) and less than 75% of their reduced deliveries (40M -> 30M), while also saying they will drop the production of Q2 massively, meaning that they expect to deliver less than 1/3 of their Q1+Q2 deliveries (from 300M -> 100M).
All while only producing from up to 2 (one of them still hasnt delivered to EU either due to AZ fucking up paperwork) of the original 4 factories that the EU contract stated (as 2 of them are producing exclusively for the UK), and actively following the contract of UK.
I will quote myself from earlier:
85% of all undelivered vaccines for EU in Q1 have been AZ(70M out of the probably missed 80M)