Nah, this is a classic case of absence making the heart grow fonder. Almunia was absoutely dog shite for most his tenure at us apart from a brief spell (when the Almunia for England noise started).
Ospina has been decent for us and saved our bacon a few times but it's been tempered by a few high profile mistakes, notably against Olympiakos.
Also the goal against Chelsea in the cup final wasn't a GK mistake per say, more that he didn't have the GK quality to save it (a taller GK with stronger wrists like a De Gea, Courtois .. could have pushed Costa's shot just wide).