The price class (based on original MSRP) is highly indicative of some base quality attributes, e.g. materials used, chassis strength/stiffness, general workmanship, insulation, etc. RV manufacturers get the price down by cutting corners everywhere. RVs in the same price range will be pretty much alike in those things and probably have similar amenities as well. Models in the mid or upper end of the price range are built using better materials (e.g. upholstery, flooring, cabinetry, electronics), have a more robust chassis (frame), better insulation, and usually better workmanship.
The wrinkle is that RV quality is inconsistent regardless of price class. Each one is essentially hand-built and things happen, e.g. a skilled guy is out sick that day and somebody fills in for him, or a worker gets behind schedule and rushes through some aspects of the job, or maybe they run short of a part on a given day and substitute something else. Even the best RV manufacturers turn out some incredible lemons on an all-too-regular basis. Thus a pre-owned RV is often higher quality than a new one, either because it was better originally or the bugs have already been flushed out.
Think in terms of a house rather than a car and you will have fewer misconceptions about RVs and RV dealers. The roof is more important than the wheels and the plumbing & electric is critical to success.