Gates always sag. I'd put some wheels on it.
My gate is made of 14 gauge 2” square tubing, is 16’ Long and hasn’t sagged a quarter inch in the 7 years it has been there. It swings over a concrete driveway and the gap is the the same all the way across just like when it was installed. It has an electric opener also and gets Used a lot. It isn’t rocket science to design a gate that won’t sag and if you use a stout hinge post and anchor it deep with a lot of concrete it won’t lean either. Mine is about 5’ deep with around 1000 lbs of concrete.