True but that doesn't really impact your ability to apply for a Green Card from TN. You have to wait 91 days [0] since your last entry before making an adjustment of status application.
Every year thousands of people in statuses like F-1, O-1 and TN get employment based green cards. The idea that you have to be in H-1B or L-1 status to get an employment GC is simply 100% false.
In the conversation of moving to the US for work 90% of visas are going to be non immigrant so saying all non immigrant visas are equivalent is needlessly obtuse.
An H1b allows the person to enter the country with the intention of getting a GC and can do so without having to leave the country.
A TN visa is re issued every single time you cross the border and can be denied by a border guard on any amount of misrepresentation
Secondly, your advice about the 90 day rule without context is both bad advice and can get someone's visa cancelled and stuck out of the country.
For future readers. Don't take this advice, ask a lawyer and if you intend to get a GC don't go on a TN unless you want legal complexity.
[0] https://www.boundless.com/immigration-resources/90-day-rule-...