I agree regarding the Comet v 707 debate going on forever but history shows that the Comet (and for that matter the Avro Canada C102) were the real airliners that set the pattern for airliners to come.
Both flew in the 1940s when US manufacturers were churning out the DC6, Constellation and Stratocruiser. Both jets had four engines, were pressurised for high altitude flight and were expected to be the initial models of long series production runs.
The fact that the Comet suffered tragedies and the Canadians bottled out doesn't change the facts.
The Dash 80 was initially built by Boeing as a proof of concept for the the bid for what eventually became the C135 and was only adapted to an airliner concept later. It followed the Comet and the Avro C102 in having four engines and being capable of high altitude flight.
It extended the thinking that had come out of the UK and Canada by offering a bigger payload and positioning the engines on pylons but Douglas and Convair, having also decided that passenger jets were the future, followed similar formats and, in fact Boeing widened their fuselage to compete with the DC8.
The fact is that the Dash 80 and Boeing benefitted from the Comet's downfall, learned from its failings and, with money earned from the C135 programme was able to fund the 707 and build them in great numbers quickly and well.
In that, then, it can be seen that the Dash 80 was a milestone along a pathway already trodden by others. Worthy of inclusion but not to the exception of the Comet.