Under Robin’s approach to value uncertainty, we would (I presume) combine these two utility functions into one linearly

It's also not clear which affine transformations of EU1 and EU2 should be considered relevant. If the question of 'what fraction of achievable utility will we get?' plays a consideration (for example, as part of a strategy to bound your utility function to avoid pascal's mugging), then EU2 will get squashed more than EU1.