It's definitely the norm, because the entire trailer weight is never on just the two rear axles.

IF you are fully loaded yet compliant (7495#) there is no way your tongue will be <495# and therefore the total weight on rear axles will be <7000#. So there is margin, just not much. I have seen trailers with 7995# GVWR and rear 3500# axles. My previous Imagine 2800BH was this way. Grand design was replacing the axles for free because it was too little margin. I believe the 2800BH now comes with 4000# axles standard or something like that.

I'm guessing you have a 2500RL like me. I am ok with these axles as they are the newer 3" tubes. Up to 2019 they used to put 3500# axles with 2 1/8" tubes (yikes!) and that's why I replaced the ones on my previous 2800BH, along with adding a CRE3000 suspension. But I'm sticking with the stock axles and suspension for now, with upgraded goodyears (before they were standard).