It’s relative. True Class B motorhomes (not to include Class B+) indeed lack spaciousness compared to larger RVs like Class As, but their smaller size also means improved fuel economy, maneuverability, and ease of driving. They are also easier to maintain and should be serviceable at more locations. And of course they can sometimes serve as a second or third family vehicle. It’s tough to compare them directly.
While much smaller than Class As and most Cs, the largest ProMaster and Sprinter vans are nearly twice as spacious in total volume as previous offerings from Ford, Chevy and Dodge that were common Class B chassis. And compared to the classic Volkswagen camper vans made by Westfalia decades ago they are huge – probably 4 or 5 times the interior volume of the original VW microbuses.
I’m personally looking forward to the ProMaster because it will be much larger than my Ford extended Econoline yet probably get better MPG. And with FWD it should drive and handle much better too due to lower center of gravity and improved suspension. The only thing it shouldn’t do better than my Ford Econoline is tow.