" There are better ways to exercise your brain that will be many more times better than Calculus. "

the ways that you list are great brain exercises but there's no good reason or research that suggests they are 'many more times better than Calculus'.

and continuing to call it a 'useless subject' is also totally unjustified. if i just that art appreciation is a useless subject because 99% of people are not going to get a job writing movie reviews for a major publication or curating exhibits for museums is that sufficient justification to say 'art appreciation is useless. source: me'?