No you have it backwards, most horses are naturally hollow right and stiff left, that is wont take as much feel on the right rein and they bend easier to the right so to speak and are stiffer left. That is in general. This is also my experience riding many different horses over many years. This is not always the case however but in general. It is even mentioned in Podhajski's Complete training of horse and rider but anyone who has ridden lots of young horses would know this is the case. It is always hollow right and like hardly ever hollow left. Trouble with the left bend is a common problem. Don't think your horse has some huge problem or you need to run out and spend five hundred dollars on acupuncture and chiropractics. I would do that as a last resort after trying to work it out with training.