I appreciate what you're saying. You should always be vigilant as a cyclist/commuter, but are you saying that when cycling along a main road you should be looking over your shoulder past every small side street? They can pop up every few metres, I'm not sure my neck is up to it!!
I'm not criticising or rejecting your comment by the way, I've only been commuting a year - cycling for 2/3, and am genuinely intrigued if I should be doing more to aid my safety.
Yeah, as others have said: When there are a lot of side-roads (or any other hazard# that requires you to control the traffic behind), the default position should be primary. Since I learned to ride in London, I learned this early (back when accepted bike training said exactly the opposite). As Cyclecraft now says: Keep away from any give-way lines at junctions you are passing!
Jez, the motorcyclist might still have done that, but lejogger would have had more room to the left to keep himself safe.

Primary stops most such behaviour, but as you say not all. It always* gives you more room to move away from the overtaking vehicle if necessary. If you are clipped on the handlebars (prepare if you think this is happening, by putting the heel of your left hand behind the bar and the fingers of your right in front and
leaning towards the overtaking vehicle) then it means you are lss likely to clip the kerb with the front (which will have you off).
*Unless you are being overtaken on the inside - that will 'usually' be another cyclists (

)
#(edit to add) Such as a brick wall or railing that cuts your escape options.