The smaller plague of 252 in this version of events is a bit of both factors; and as there is more stability beforehand and Rome has won the battle of Abrittus more decisively in 251, leaving the Goths minus more warriors and minus warlord Kniva, the Roman army is stronger and some of the actual invasions of the mid-250s do not happen due to the invaders being put off attacking by the Roman success. This has long term results - there is less need for campaigns in the Balkans distracting the Rome regime.
We do not have much idea of the actual numbers or scale of losses to the plague, unlike the Justinianic plague of 542, as there are fewer and vaguer sources plus a subsequent series of military disasters that may or may not have been exacerbated by losses of soldiers and taxpayers. The teenage emperor Hostilianus and considerable numbers died in Rome, so it was presumably hitting large urban areas badly (sounds familiar from 2020 events). The armies facing the Germans on the Rhine and Danube and the Persians in Syria were also overwhelmed easier in the later 250s than they had been earlier, there was popular support for Valerian turning on the Christians plus local initiatives in rounding them up (ie panic over their insulting the gods who needed to be appeased?) and when Valerian needs more troops for the Syrian campaign in 258-60 he has to call on soldiers from the West so logically the army in the E has lost manpower. All this implies considerable disruption, though the enemies of Rome would be emboldened by the 251 disaster at Abrittus anyway. There was also a rash of pretenders even ahead of Valerian's capture, and a willingness by the Rhine army mutineers to risk challenging an incumbent adult military Emperor (Gallienus) and to kill his son and heir - so logically the rebels thought the central army was too weak to stop them?
My overall idea for the 250s is to diminish the number of simultaneous problems for the Empire and so make it easier for the central regime in Rome led by Gallienus in 260-8 to hold on better, with more soldiers, to more territory (eg in this version it holds onto Egypt with its corn and tax-revenues; in reality it loses these to the Palmyra regime). Crucially, I have less German invasions of the Balkans and the Austria-N Italy route than in reality, and less Imperial time spent fighting there - which is partly due to the long-term butterflies from Rome holding onto the lands N of the middle Danube (Marcomannia/ Bohemia and Dacia/ W Rumania) and having extra troops from there. Thus an earlier and stronger recovery in the late 260s and early 270s - while keeping to the basic actual timeline (with tweaks en route) to just before Aurelian's death in 275 - when things in my version change more. Dependant on availiability of space within the word-limit, my book on the period from 180 to the C6th will expand this basic timeline. But it is not giving too much away to point out one continuous theme - a stronger, or luckier, West than in reality.