I suspect your furnace and ducting is fine. I'm currently out in my 26RLS and the furnace takes about 20 minutes to bring the temp up 7 degrees. These trailers are really well insulated, so a large furnace isn't required to maintain a comfortable temperature. In fact it hardly ever runs even though it's 45 degrees outside. A larger furnace could bring the temperature up more quickly, but would probably end up short-cycling, which can cause reliability problems.
I don't have a cabinet vent in the bathroom, but the floor vent there does seem to put out more air than in the other spaces. As others have said, the air flow is pretty low, but it is hot. In fact that's a bit of a problem if you walk around in bare feet. I came close to burning my foot once when I stood on the vent in front of the stove.
2017 Outdoors RV 26RLS
2015 F350 6.7L