Then the next question is - can the tip's speed and direction with a swoop stroke be duplicated using a straight stroke?
The answer is obviously yes - so why would you ever swoop?
Go for it! Turn your cue slightly diagonal, now backstroke with the whole cue held diagonally in both hands, to preserve the angle, now come forward, getting the english you like. Give it a go! (I'm guessing you didn't and stroked with your mind, not testing the technique at a table.)
The problem, of course, is you are now punching into the globe, knocking it over, instead of slapping it obliquely, "riding the circumference" as was stated above--if you can execute the stroke you are requesting above, that is, turn the cue diagonal and bring the whole works back and through, while angled, instead of stroking in the direction the cue tip points!
Put another way, I'm comfortable shooting pivot (a diagonal stroke hand movement) or carabao (forward with a bit of deviation) but not brooming a diagonal cue stick with precision.
Or put another way, you're right, and many of the pros in the world are wrong--who have been backhanding for a century or so. I'll say that at the risk of invoking an ad populum fallacy.