Likely, there must be a difference between a rather sudden large jump in the temp and an increase of the same magnitude but a slow one, during which the fish can gradually adjust it's body and blood and gill chemistry and physiology to the gradually lessening amount of dissolved oxygen.
IDK about wels but some fish enlarge their gills/their gill area/capacity by growing extra feathery protrusions on their gills in response to a lessening oxygen concentration... but these fish have evolved in harsh tropical environements with large water level fluctuations and a long drought season, so I am thinking of this just as an example. Perhaps other fish from more stable environments, like wels, have some strategies like that only to a much smaller degree.