I specialized in sorting out how to get regulations from two (or more) different agencies to intersect in such a way as to make it impossible to comply with either/all of the requirements.
Except that the EU's Directive and the UK's "visas", are both tick box exercises, athough they have different ways in which they are implemented.
The EUs Residence Card does not give the holder any rights as these cards are merely declarative. If the EEA citizen is being an EU "qualified person" at the time they apply for an RC, then they and all their family members get an EU RC for that country. However the EU's RC is given in expectation that the EEA citizen (their EEA citizen sponsor) will remain a "qualified person" every day, as required under the EU's Directive.
If the EEA citizen fails to follow the Directive/ stops being a "qualifed person", then their RC become invalid as does the RCs of all their family members who they sponsor. Any non-EEA citizen family members they have, have lost theiir right to work (and live) in that EEA country. The end date on the EU's RC means nothing as these cards do not give the holder any rights.
Whereas unlike the EU's RC, the UK's "visa" gives the holder rights. Those who lose their sponsor can still live in the UK with the same rights their visa gives them, until the end date of their visa. i.e. work, bill free use of the NHS. They remain lawfully in the UK until their visa ends.
That lawful time in the UK for those on a "visa" can be extended after their visa end date, with the same rights their visa gave them, if they put in a valid "visa" application before their visa ends, They can do this under 3c of the the UK's Immgiration act 1971. This means they are not an overstayer. The EU Directive does not have anything like this.
It's quite simple.
Two different routes and foreign nationals must follow the rules of the route they are on. The UK does not regard an Irish citizen as a foreign national.