I don’t think the Caighdeán is hated because it simplifies the language. It is mostly disliked because it’s not a true dialect in the most meaningful sense – that being that it is not spoken by native speakers. People who grow up speaking the language speak a real dialect from a real place, not something that was codified by academics to meet the needs of official use. That said, I don’t think if you speak it you will encounter actual derision from native speakers. It seems that for the most part people who speak Irish currently accept that many if not most other speakers they encounter may be speaking a different dialect than them or may be using the standard because they learned it in school. Also, the Caighdeán isn’t really, in it’s truest form, an Anglicization of the language. That is currently taking place, but not because of the Caighdeán but rather because of language contact with English and the fact that more people are growing up speaking primarily English but also being exposed to Irish through non-natives and thus they are learning ways of saying things in Irish based on English calques.
With regard to dialects, it is much more than pronunciation. There are different words that are used for certain things in one dialect that have a totally different word in other dialects. There are different verb forms, different rules on consonant mutation, different ways of forming plurals, sometimes the gender of nouns even changes.
By the way, if you’re looking to stay in CeathrúÂ Rua and want a nice Irish-speaking B&B, I recommend Carraroe House which is run by a lovely woman who makes a great breakfast and speaks native Irish very well. I stayed there for a week and haven’t eaten so well since then.