A motorhome is still going to bounce around on rough roads. A DP with an air ride suspension is going to be better than a gasser, but both will bounce around and shake rattle and roll when on the really rough roads.
There is a long list of why one is better than the other with good things on both sides. I can tell you the main deciding factors for me in going to the Class A over the truck trailer combination was a few things. One is I had no need for a monster truck and I wanted a good size RV. So if I went with the 5er I'd have needed a 3/4 to 1 ton big truck. I just don't like driving a big truck around as a daily driver and I surely couldn't afford to have just bought it to pull the trailer and nothing else.
Number 2 for me was cost. A Class A DP was cheaper for me. Now that may be confusing for some, but I'm not a cash buyer. If you're a cash buyer than the truck trailer deal may be good for you. But I had to finance. To finance a $45k plus truck is going to be a really high payment over maybe 6 or 7 years. You can get a longer payment term on the trailer but the two payments combined (for what I would have wanted) would have had a net cost more than the class A DP. That's because I got a long term loan and 100% of the interest on that loan is a write-off as a 2nd mortgage. On your truck-trailer combo only the trailer loan interest is a write-off. In the long run I'm going to pay more, but I got a cheaper net payment for the fist half of the loan.
For me, those were probably the biggest reasons for the Class A over the 5er, but the other reasons already listed played a part too. I love sitting up at eye level with the big rigs and being able to see down the road ahead as well as getting a better view of the Country as you drive by.