The V10 is indeed a workhorse, although my opinion of it is much different. I do agree that it's very loud at higher RPMs. Mine has 147,000 miles and still going strong -- granted in a smaller and lighter van and not a motorhome twice as heavy or as large to push through wind. On my previous Class C or many Class Cs I've rented the V10 seemed to work OK but always loud if higher RPMs were needed to develop power. In my lighter van noise isn't as big an issue because I rarely need higher RPMs due to much lighter vehicle weight.
The Ford V10 has a long stroke relative to piston diameter, making it better suited for low RPMs. A 90-degree V10 is not inherently well balanced either, so it's no surprise it feels rougher at higher RPMs than a comparable V8. Some engine designs like inline-6s and V8s are inherently smoother.
The 2-valve version in E-Series makes 305 HP which is only 45 HP per liter. By modern standards that's so low that it's no wonder they last a very long time -- which is a good thing.
Personally, I'm not so in love with this V10 that I feel Ford shouldn't replace it with something better. It's OK for now but I can't wait until Ford offers an equivalent V8 to see if it's smoother and quieter, particularly at higher RPMs.
In the context of your question, I would not hesitate in any way whatsoever buying a motorhome because of the V10. It will likely last longer than the motorhome itself. But in my opinion it is a truck engine that is not refined to modern automotive standards.