Class C Motorhome Reliabilty

Motorhomes probably break down "a lot" because people let them sit unattended for long periods of time. Many probably do very little to prepare them for winter storage. Then, in the spring, they get fire it up and head out for a couple thousand mile trip only to discover something's wrong.
Any large vehicle: truck, motorhome, etc. that is being asked to haul and/or tow lots of weight needs regular maintenance to perform at it's best.
The drivetrain in a class C is no different than the standard van or truck it's based on. Given proper maintenance it should last just as long.