My last class C had a full bunk over the cab with no forward facing bunk window. It did not have a full fiberglass cab over like the current one does. Never leaked as far as I know. I think those windows were a major leak source.
Also older units had wood framing. Both of my units are/where aluminum framed. Another positive change is some manufacturers are using materials inside that are not damaged by water in the cab over.
My current unit has a shortened fiberglass cab over because I have an “intertainment center” there that I never use. It still has a heck of allot of storage behind the TV that lifts up to get to the storage. The “B+” units do not have that amount storage. But they are more aerodynamic they say.
The last thought is all RVs need regular exterior inspection when it comes to anything on or connected to the roof. I had a class A with a front cap leak when I bought it and did not see it for several years. Old caulking seams are deceiving.