In some ways, yes. The Class A chassis is purpose built for carrying a motorhome body and designed with more capacity and better rigidity than the van chassis used in most C's (other than Super-C truck chassis). That in turn usually enables the RV body builder to do a somewhat better job of laying out the plumbing etc. And yes, some brands are built better than others, driven by the target price of the rig. If one RV is $20k cheaper than another of similar size and amenities, you can bet they skimped on the quality of materials and workmanship.
Where they are all largely equal is on the number of goofs on the assembly line and the amount of design flaws. Even the best and most expensive rigs seem to suffer from sloppy work, inadequate engineering and poor quality control (inconsistent results on the assembly line).
You can't really generalize, though. There are a few well built C's and some cheaply built A's, and on any given day the best manufacturer produces some real lemons.