The original concept that bees shouldn't be able to fly used the physics at the time - and applied rules relating fixed wing areas to body weight. Under those rules, a bee would indeed be unable to fly - but as has been explained, the bee's wings are not fixed, and are able to generate enough fleibile movement to displace sufficient air to proel the insect off the ground and through the air.
The original theory was offered by Tom Baker in a 'Doctor Who' epidosde, and I, along with millions of other impressionable viewers, took it to be gospel, and quoted it liberally.
To be fair, if memory serves, the good Doctor opined that a bumble be 'should not be able to fly' - which using the original theory is a correct statement.