Minimum requirement for a stabilized approach is 500' VMC and 1000' IMC.
(if you have personal or company standards that are more conservative, that is fine - but they do not apply to anyone else).
Was this situation VMC? Yes (Iberian pilots reported "excellent visibility conditions" and both aircraft saw each other, and the tower saw both, at >3 miles).
Therefore, the aircraft's speed and configuration can only be judged stabilized, or not, below 500 feet AGL (and roughly 1.5 miles from touchdown). Speeds and other factors above that altitude are irrelevant (although they may violate other criteria, such as speed within 5 miles of the airport).
Was the airplane's speed stabilized below 500 feet? The standard is - not below Vref, and not more than 20 kts above Vref. Therefore the crew has a "window" to decelerate as much as 20 kts in the "stabilized approach zone" (between 500 feet agl and the threshold) while still meeting the criteria for a stabilized approach. Therfore, being at 174 kts passing 500 feet, and decelerating to 155 kts at the threshold, would still qualify as a stabilized approach.
Did the aircraft exceed that range below 500 feet? We cannot tell for certain, since Vref would depend on information not available - weight, and flap setting. Someone can probably calculate weight fairly closely, based on fuel burn Orly-Tenerife, and cabin loading (153 pax). And flaps can probably be assumed to be 3, since the crew mentions specifically that it was "common" to use less than full flaps at Iberia (as well as decelerating approaches).
Presumably someone with A321 figures can give a good estimate of the weight, and thus the Vref for flaps 3 in this case. If that was exceeded by 20 kts any time below 500 feet, the approach was not stabilized. Otherwise, it was.
Equally presumably, the investigators DID have the numbers needed. They had every opportunity to point out that the approach was not stable, if such was the case. They did not.
Personally, I agree with the Iberian crew decision (in the absence of ATC input) to continue the landing on the same grounds they did - that two planes in the air at 1250 meters or less (and with neither having sight of the other) is more dangerous than a separation bust with one plane airborne and the other decelerating on the ground.
Had I been the controller, I hope I would have called both a take-off abort AND a go-around while Jet2 was still getting lined up.