People always throw around this "it's just preference" bs, but it's really not. It's mechanically different and requires different muscle movements altogether. As for whether it's better, I believe tablet is objectively better. Otherwise the top ranks would not be dominated by tablet players, even though almost everyone has been using a mouse since they were young and a tablet for at most a few years (unless they do art etc). Although you could argue that writing muscle memory carries over to tablet, it doesn't really, besides the very basics of holding a pen, osu requires generally larger movements and such, yet people without any art background still switch to tablet and many see improvement.
As for reasons for the tablet being better, in my opinion it comes down to several factors:
1.) Weight, simply put, a tablet pen is almost always going to be lighter than your mouse. Lighter objects move faster, it's physics. It also means changing directions with the pen will be faster, important for back and forth movements.
2.) Ease of "grasping" where the center of mass is. With a pen, the tip of the pen is where you're pointing, it's simple, it's intuitive, your brain will just get it naturally. A good mouse will have the sensor at the center of mass usually, but it still feels less precise in terms of your brain registering in relation to what point you are moving the mouse. Basically it is the difference between drawing with a stick in the ground and drawing with a rock. The rock just
feels less precise. Whether or not it actually is, is another matter, but I feel that this makes retaining muscle memory of the aim more difficult for the mouse.
3.) Absolute positioning makes muscle memory easier to retain. This is a pretty major point, and is often mentioned. Basically the tablet player will always be aiming at the same spot on his tablet for the same spot on the screen, so patterns will always require the same set of movements. On the other hand the mouse player could have his mouse in a completely different position on a different play-through doing the same pattern on the same map. I don't feel that this makes much difference just sight-reading maps and such but for repeated play-throughs trying to farm maps etc it can make a difference. And of course, as mentioned already, no mouse drift to worry about.
4.) Moving the tablet pen can be achieved using smaller (and thus more precise) muscle groups than the mouse. I feel that this point is rarely (if at all) mentioned but in my opinion is probably the most important point mentioned here. Ok firstly let's see how you would typically move a mouse. There are three major grip styles: the palm grip, the claw grip and the fingertip grip. For the palm and claw grips, most of the vertical (up-down on the screen) movement is achieved by moving the arm, with some smaller movements by extending the fingers a little; the horizontal (left-right on the screen) movement is generated by and large solely from wrist movements. Now the major problem is that you are using mostly arm and wrist muscles which are generally less precise than the fingers. But hang on, what about fingertip grip? Surely that's just fingers, right? Well, no... Sure, you can do 100% of the vertical movements with just your fingers, but the horizontal movement have to again largely come from the wrist. Just try it yourself, try to plant your wrist completely and keep it still and move just your fingers and see how far it can move a mouse horizontally. Meanwhile a tablet pen can cover a moderate active area with just mainly the finger movements (with the wrist planted firmly) of course with some hand rotation from the wrist and such. Sort of related to all this is the fact that most people are using a mouse DPI which would translate to an "active area" which is smaller than what most tablet players are using, while still using larger muscle groups for these movements, which often results in less precise movements in the end.
In conclusion, I don't believe the "potential" of mouse is any lower than tablet, even though it sounded like I'm just completely shitting on mouse. Even with the drawbacks, I believe the top potential of mouse is just as high. But the only difference is that, it most likely will take many players longer to reach their same maximum potential with mouse than with tablet, because tablet is most likely easier to improve with due to the reasons discussed above. I feel like I may have missed another point or two, but well, that's all I could think of right now and ended up being way too long anyway