Size, differentiation and readability are typical usability issues and not aesthetic problems. Even though I personally think that both terms overlap in meaning to some point (because attractiveness catalyzes the acceptance and therefore affects the usability) for clarity in such discussion I think they should not be mixed:

Usability = ease of use
Aesthetics = attractiveness

And I totally agree with you – usability factors should never be sacrificed in favor of aesthetic factors. They should be supported by them. But again, a professional should know all that.

/Aesthetics IMHO are always subjective.

No this is just very popular delusion. Applied aesthetics and people working in that area study and employ the popular/group reaction to visual problems. Not the individual characteristics.