Those who have argued it is not high risk is just because of supposedly good ventilation on planes, and anyway it's relative risk. Of course it's best to limit time indoors with others, to as little time and as few people as well one can endure I guess.
But the average plane may be no more risky than the average office, which probably has quite poor ventilation indeed, just one may have a lot more choice about getting on a plane than going to the office.