Where are you getting this understanding? You are asking for evidence while providing none yourself...
I'm not sure the concept of "burden of proof" is helpful in a collaborative fact-seeking discussion. It seems more relevant to adversarial debates and trials.
It’s not clear that “avoid elevators” is universally less harmful. Also given the 15 minutes suggested it’s not clear that elevators by default pose a risk, and the large numbers in use in the world make it surprising if they are indeed a major vector but are otherwise undocumented or not part of suggested guidelines thus far.
I’m asking for evidence which shows they are indeed a risk factor, which should also hopefully take into consideration mask usage and number of stories. This would be extremely useful for people to factor in if they need to move, for example.
You've claimed that elevators are an exception to the established guidelines without evidence and are now claiming that that other, well evidenced, claim some how needs additional support to be applied to elevators.
It may negate the safety of the actual airplane trip, or it may not.