There are mitzvos concerning protecting one's health and well-being that must be considered. Sitting on the knees can damage them. Bare- foot exercise can injure the feet. Extended isometrics, which are fundamental in several schools, causes circulatory problems for those over 30. Conditioning techniques can cause bone and nerve damage.
Some teachers present unacceptable attitudes toward the use of force.
If Abaye is Rabbah's brother's son, then yes. If he's Rabbah's wife's brother's son, then there's no blood relationship at all. Nevertheless, you point regardin public tzedakah work is well taken. I don't disagree with that at all.