This is what’s interesting about a board like this with different posters and different opinions. I would not take any particular post as gospel, but read all of them and come to your own conclusion. I’d had cars where the park/emergency brake would lock up the rear wheels and cars where the properly adjusted and maintained park/emergency brake would not lock the rear wheels. One thing for sure is that you should at least feel the brake try to slow the vehicle down somewhat. If it doesn’t, then perhaps the brakes or cable needs adjusting/replacing. You can talk to 3 guys who have over 30 years of wrench turning each and I promise you’ll get three different answers, so experience is not always a good indicator for a question like this. When a manufacturer comes out in the owners manual that says the park/emergency brake is supposed to lock up the rear wheels when applied at 30 mph, then, and only then will I change my opinion. But we both know that ain’t happening.