IMO, it's not normal to have suspension issues or replace parts within the typical use time, although some owners have issues immediately.
The sad truth is that the typical frame and suspension are engineered to carry the trailer weight at the maximum of their ability. Mfgs put the cheapest tires and components together without thought of wear or possible stress to the suspension or frame.
FWIW, when I bought my old Starcraft, the first thing I did was to get underneath and see what it had for frame and suspension. I knew it had deteriorated wood frame issues with the body of the trailer but it was important to me to have an adequate frame and suspension. As it is, I am now using the restored trailer with it's original suspension and frame. I have torsion axles, shock absorbers, and a full boxed frame. The trailer is 45 yrs old.
I did replace the mixture of tires that were on it when I got it. It has a set of new Carlisle's, now, and tracks like it is part of the truck. The brake wiring, as has been mentioned, was replaced into a Star configuration. I'm happy with how the running gear is performing.
Good luck with a future trailer purchase. I wouldn't let bad reports of running gear dissuade me from a purchase.