Re: Zazen necessary for training
When I trained in the UK, I practised zazen on a regular basis for 90 minutes before class. At that time the zazen training was led by a zen master, so our training was directed. One of my early aikido teachers, who is now a Buddhist priest, also recommended us to practize zazen because he himself practised. However, he actually began to practise zazen because his postwar education in Japan had disposed him to reject the shintoist training that O Sensei practised (even though he was one of the Founder's deshi).
My teacher's father-in-law, however, eschewed zazen in favor of individual training (for example suburi training) with a sword, on the grounds that that kind of 'meditation' was more immediately productive and relevant to aikido training. He told me that O Sensei had said, 'Ken before zen" (not, of course, in those very words), but I do not think son and father-in-law ever agreed on this point.
When I came to Japan I stopped practising zazen because I could not find a good teacher, for I think serious zazen training requires a teacher.
Best wishes to all,