The depth of field effect (and possible other effects?) gets progressively less and less pronounced as you increase the resolution. I wonder if the effect could be scaled to compensate. This was already a problem in the HD collection and increasing the resolution past 720p makes the issue even worse.
720p:

1440p:

PS2 (for reference):

Fixing this kind of stuff could turn this version into the definitive edition of the game
(if you do make a fix for this it should ideally be optional as I'm sure many people prefer the cleaner look of no DoF)