As a cyclist who has played a reasonably significant part in the cycling community in recent years my take is...
STAY AT HOME!
Trying to justify exceptions for one activity over another is not what everyone should be doing at the moment. The authorities, experts, police etc have made it clear that they want people to stay in as much as possible. An hour outside doing the permitted activities is enough. The self isolation argument falls down when every man and his dog drags a bike out the shed and the place ends up like Box Hill on a summer weekend. In so doing there will be more accidents and more contact. Then the walkers will want to stay out, then the runnefs and before you know it every mother fucker is outside enjoying a 6 hour leg stretch.
It is currently a 21 day lockdown FFS just play the game that the authorities want and stop bellyaching and spouting self indignant justification for your own activities exception!