It is not always necessarily the best. But certainly later copies shouldn't hold as much weight though they have been in the majority for the most part after 1000 AD.
You know Erasmus didn't use any manuscripts (my umbrella term) before the 12th century? Wouldn't documents of the 2nd to 6th century be considered valuable?
Yep. But since when is textual criticism higher criticism? Textual criticism has been practiced for a long time. It's necessary. Don't call good evil.