I've driven or ridden behind quite a few Harley's since 2009 with these rear lights, and at least in daylight I definitely see a difference compared to the "old fashioned" solid red lens incandescent bulb tail/brake lights. I also have noticed the same thing with many cars btw. Somehow the manufacturer's have been able to meet the minimum DOT requirements with the cutesy new tail/stop lamps, but at least to my eyes they are NOT as obvious. The smoked or clear lens units seem to be the worst.
Even if yours are working normally, I'd still recommend adding more lights. Unless you always run a Tour Pak, which is the ideal location for additional lighting, you could at least add the lights that are available to your bags. IMHO you can never have too much lighting on the rear of the bike. Maybe that's because I've had the severe displeasure of being run over from behind in the past.
Jerry