When you are becoming a doctor, you have to practise certain treatments like intubations, setting up an intravenous infusion or even basic surgical skills on a living person at some time. How else are you supposed to learn how to do it? That's the truth and it has been like that for ages that you have an experienced 'teacher' guiding you through it and assisting you.
The same applies to our beloved profession: how are you supposed to learn how to operate your aircraft in all kinds of phases, WX etc. if not under realtime conditions under the supervision of an experienced person next to you?
The art is to truthfully realize and acknowledge when a situation becomes critical, demandig the person in charge to take over and to accept that now the instruction time is over.
The LH-guy in Hamburg would have been better off to fly the approach under extreme crosswind conditions himself.
Capt. Sullenberger on the other hand quite naturally claimed his right to assume control in a potentially desastrous situation (I do not want to imply that his F/O wouldn't have been able to the same!). We all know the outcome.