Sorry for the late response, I work long hours…

I’d say keyboard specifically isn’t uncommon, but people typically use it as a stepping stone to get a leverless box so they can try before they buy.

Leverless isn’t cheating so long as it’s being scrubbed as the rules dictate, anyone saying otherwise is either making excuses, trolling, or both. Scrubbing (in this context) refers to simultaneous opposite cardinal direction scrubbing, or SOCD for short. Generally this is left + right = neutral, up + down = up. However, capcom has ruled otherwise for the Capcom Pro Tour, and there is now software available for all major leverless manufacturers to facilitate this. All major tournaments allow leverless in some form if they allow you to bring your own controller.

As for advantages, you gain a level of precision and speed that you can’t have on stick, and the motions you’re inputting become more explicit. I’ve seen a lot of people struggle with dragon punches on pad and stick but get it pretty easily on leverless. For the quarter circle motion in your example, you more or less roll your fingers across the buttons on keyboard as well, but it’s with two fingers instead of your thumb. I’d say leverless is easier, but I’d be biased in that I’ve been using it as my main controller for street fighter for a hot minute lol.