Horizontal Recoil on Mouse vs Controller
I use both mouse and controller.
There is almost no horizontal recoil and drift when using a mouse vs controller.
The controller has a deadzone so the horizontal recoil drifts uncontrolled freely within that deadzone. You need a deadzone on the stick or else you have stick drift. The slowdown (aim assist) doesn't help with this, it makes it worse, because it slows down input so technically the deadzone becomes larger or more sluggish.
On a mouse you have almost no horizontal recoil because the mouse doesn't need a deadzone so your input is constantly keeping the sight in check whenever you slightly move the mouse.
Then on top of that Respawn may balance the game additionally in favor of mouse input by having the weapons with highest damage have the worst recoil.
"Competitions"
Because of this difference, tournaments and competitions in Apex Legends can't be considered as a competition. It can be considered as entertainment, but not a competition.
It's as if Nadal showed up agains Federer with a table tennis racket. It would be entertainment, but not a competition.
I know Electronic Arts wants to promote their games as a sport, but as long as there is crossplay its not a true sport. The terms are different. Its only entertainment and thats ok.