Actually only for photographers who continue to use old stuff.
If you use gear which is current, backward compatibility never becomes an issue.
Hmmm, I don't see why users of new lenses can't have any fun with their gear. Who says you can't find out what is the optimum aperture with new lenses? I'm having a blast with my AF lenses and I seriously will never go back to using legacy lenses on a regular basis not because they aren't capable of producing a sharp image but rather because I like to shoot quickly and get far, far more keepers with current AF lenses. I seriously question your assessment that one will get "standardized" photo style.
Sure there is definitely a place for shooting in Manual mode when you need to take creative control. But it is stretching the argument to say automation (AF, AE, etc) detracts from having creative control. So long as the photographer knows the variables determining exposure and know how to best use the different exposure and metering modes, he or she can use any metering mode or exposure mode to get the shot.
Sorry but whenever I hear people say that one has got to use Manual all the time, I can't help but feel that it is a silly advise imo. People had to shoot mostly in manual in the past because cameras back then barely offered any form of automation. I've met my fair share of photographers who are too entrenched to change old habits or stuck in time, or buy into the notion that one must be shooting in Manual mode most of the time to somehow raise their level of photographic competence. How many times have I heard people say it will make you more creative... humbug.
To me cameras today are multi-functional/multi-dimensional tools. Different people can use the same camera to get different results or use different features to arrive at the same result. Automation is a great timesaver and a technically competent shooter knows how to exploit the benefits fully. Nothing wrong to shoot Manual mode all the time but it's like driving a supercar to church on Sunday at 30kmh in first gear - you're just not capitalizing on its full potential or worse, you're just limiting yourself.