For many many years I had the older version of the Olympian heater that is the exact same as the Wave 6. I think it was model 600.
At this time they were made by US Catalytic, way before they were part of Camco and before they had an optional low-oxygen cutout feature. It was in a 10.5' 1967 Travel Queen camper.
I paid about $550 of early 1990's money for it, made in the USA with a fitted cover. A small fraction of what they go for now so I don't know if there is a quality difference now that they are Camco and made who-knows-where.
I had a window in the back door of the camper I would open about 2 inches, and I would crack the cabover vent about an inch or so. I never camped in extremely cold weather but at least to the low 30's (frosty) that heater easily kept it very warm in the camper with 1967 insulation and single-pane aluminum windows. You couldn't turn it below "low" so I would just open the window/vent further to throttle the temp down when it got too warm. I ran this setup for almost 20 years.
Unless the output power is many orders of magnitude worse than they used to be, I think there is something wrong with your heater. From what I remember of mine, it would pump out heat like sitting next to a campfire.