As someone who has done 'masters' events in a couple of sports (although not cycling), I think it is important to state the obvious and say that a Master's World Championship in an age-group category is quite different to a proper World Championship. At a master's event, there tend to be relatively few competitors in each category. Competitors will be self-financed and responsible for their own travel and accommodation and this tends to limit participation. Successful older athletes (i.e. those over 35!) tend to have retired from the sport, too.
Looking at the website for the UCI World Championships 2018 held in Los Angeles, it looks like there were just 8 other competitors in McKinnon's event. Indeed, it also looks like there were so few competitors that they merged the F35-39 and the F40-44 categories.
In total, and across all women's events and age groups there were fewer than 100 cyclists competing. The video of the competition is on the website. There are almost no spectators and the velodrome is empty. The link is here: mastersworldsla.com/
McKinnon's fastest winning time was 12.554. In the equivalent men's race, it was 11.227. McKinnon would have come dead last in the heats of the M35-39 sprint.
There is a considerable difference between calling yourself a 'World Master's Champion' (although McKinnon tends to leave out Master's) in an event with only eight other competitors and being the best tennis player in the world for many years, winning countless Grand Slams in a truly global sport like tennis. I had the pleasure of watching Martina Navratilova play at Wimbledon several times and she was an incredible - truly incredible - athlete.