Depends on the major. Accounting is a pretty legitimate degree with high-ish earning potential. Finance can be semi-legit, but most Wall Street jobs will just as easily take people with math or engineering degrees, often preferring them, and those degrees are way more versatile. Most others will not increase your career options. I made this mistake sadly.
I have an undergraduate business degree and I have done very well with it. Your mistakes are your own, don't blame the program.
What was your major, and what type of job/position did you take post-undergraduate?
I think you do a disservice to young people by giving them absolute advice like that. Business school does not work for everyone, that does not make it worthless or only good as a supplement.
My degree opened doors to a career that I would not have with any other degree. That doesn't mean everyone should do it but a lot of people can. It certainly means that your absolute statements are incorrect.