I’m not a specialist but I believe that’s exactly what devices like the Cronus do (among other things): so from an official standpoint, it would be considered cheating and could lead to a ban.
For a more hypothetical discussion about fairness: yes, it would be unfair, albeit until it isn’t. Let’s take slowdown as an example: a big part of aiming skill is the final adjustment just before your aim reaches your target. Everybody can easily learn to move their aim with great speed towards the general direction of a target, it’s when you get close and you need to slow down that skill really comes into question.
A good player will barely slow, and yet the aim will stop to rest right where it should be. A worst player would need to be more deliberate, slowing earlier to make sure they don’t miss. Me, a very average player, I can go quite fast but somewhat regularly I will under or overshoot: my aim will stop just a bit before or just after the target.
With controller slowdown, that problem kind of goes away: you can set your mouse for full DPI, swing full speed, and the game will automatically slow you down as you get close to the target, facilitating the last adjustments. If well set up, it would make a beginner immediately better than a large chunk of the m+kb population. That’s clearly unfair.
But note the interesting bit is that it also imposes a ceiling on skill. If someone was good enough to maintain full speed throughout the entire process, they would now be slowed down by the system despite not needing the assist.
Anyways, controller assists are there because controller are inherently worst than mice at making fine adjustments at speed. As such, using them with a mouse is obviously wrong, as you’re stacking the advantages of one with the extra support for the other, considerably reducing the skill gap.
