My experience is as a parent in another country, but since IB is a standardised international education system, my comments may still be relevant.
My eldest attended a private school with a middle primary program which is the prelude to IB, whilst the daughter of one of my best friends, who is a few years older than my daughter, was enrolled in IB at the same private school. IME, your concerns are valid - my friend’s poor daughter was up until 11pm every night, doing homework and trying to complete assignments. At my friend’s request, I helped her daughter with a couple of her assignments and from what I could tell, she was so busy and tired trying to complete tasks that very little knowledge was actually sinking in. This was one of the driving factors for me to transfer my eldest from that private school to the public school system, where her siblings enrolled from their start at school.
The other aspect of IB that I would take issue with (although I don’t know if this applies at all schools) is that the assignments were sent overseas for standardised marking and feedback was received months later, by which time some students had lost interest and therefore did not gain benefit from the feedback.
On the other hand, my son has always been a self directed learner and I did wonder if the IB program would have suited him, however he did well in the public school system so we have no regrets. It may largely depend on what other options you have.