Same here. My max HR is high 160s. My typical long distance racing HR is around 140. I can maintain low 150s for a little while. For example climbing. When I hit high 150s then the clock is ticking and if I don't back off I know I'll blow.

This- if you are maxing at 160.
Riding most of the time at 135-150 is way too hard.
Get tested or figure out how to test yourself and set zones.
Don't worry about a low heartrate. Heartrate by itself is not an indicator of performance or potential performance.