I mean, I like the idea of Tails mindlessly following you like in Heroes. That sounds really wacky. But come on, custom 1? Wanting to incorporate button slots made for custom characters into vanilla is not viable at all.
Honestly I disagree, and in fact I still haven't really seen a convincing argument as to why this would be the case. In particular, you would need a third button to properly make use of a more accessible Tailsbot assist. Otherwise, it would conflict with other actions, whether that be jump, thok, spindash, or shield abilities. Following a strict two button formula is incredibly limiting, and even the newest of players shouldn't have a problem comprehending use of a third button to perform certain actions.
It doesn't specifically HAVE to be custom 1, but custom 1 is already an input programmed into the game so I don't really see the point of mapping such a thing to an entirely new and separate input just for the sake of differentiating from addons.
Changing the behavior of Tails does not solve the issue either. No matter how you set Tails up, Sonic is massively weaker than Tails and Knuckles for the core single player experience. Sonic alone is also an option that completely ignores your suggestion. The problem is presenting the thok to newbies. Addressing something else isn't going to solve that, regardless of how effective Tails becomes as an assistant.
I don't really see how Sonic is "weaker" in the core single player experience at all. He doesn't have as much vertical mobility on his own, making him more difficult for skipping sections (And in fact almost entirely preventing him from doing so), but getting higher times doesn't make a character "weak". Horizontally, he's the most mobile out of the main trio as he can go from a full stop to full speed instantaneously, allowing him to more easily avoid attacks by moving himself out of the way.
In addition, if Tails and Knuckles by themselves are not considered problematic for a new player, then I don't really see how making Tails Assist more catered to new players fails to fix the problem. It adds to Sonic's options in a way that is constructive for either navigation through a level or for merely correcting the player's mistakes, similarly to how just playing as Tails would. The way I see it, Tails assist would be like training wheels. Sure, first time players
could decide to just play as Sonic alone, but I really just don't understand how this is even a problem. That's a conscious decision the player has made on their own. If they are having trouble, they have the option of switching to the &Tails combo. If they refuse to even consider it and leave a sour review, nobody takes them seriously on account of them not giving the game a fair shake. People looking at game reviews generally aren't stupid, they can tell when a review isn't fair.
If the topic of discussion is merely just the
presentation of the thok, there's a lot you could do to improve on that. You could showcase skilled gameplay of the thok on youtube (or hell, even do a series covering each character to really show what they are capable of as advertisement) to show potential players what they might be able to do themselves eventually, you could cover the thok more in depth in the tutorial, you could include an additional warning on the character select that Sonic is a more advanced character and that the &Tails combo is more recommended for beginners when the player tries to select Sonic alone the first time, etc.
I feel like the fear of new players making poor choices is rather misplaced. Players don't need to be babysat. If they don't make mistakes, they can't learn from them. You seem to selectively understand that when it comes to some aspects of the game as opposed to others. If players quit the game because of their own poor choices, that's not the fault of the developers. If players insist on playing as Sonic as their first choice because he's the title character and insist on playing as him without Tails (Their training wheels), then if they mess up that's on them. It's like learning to ride a bike. If you choose to do it without training wheels, nobody is going to take you seriously when you blame your problems on "This bike sucks" and nobody is going to complain about the bike manufacturer when they see the poor review.
A more accessible Tails assist presents the opportunity for a player to learn the thok in an environment in which they are safer. Every veteran was new at some point. If we stuck around this long, then there's no reason why other new players given even more options than we did for learning it can't stick through it too. That's not to say that the thok couldn't use tweaks, just I really don't feel like the thok itself is as big of an issue as it's being made out to be. In general the thok is mostly being reported on as being enjoyed, the community therefore is well aware of what the thok is capable of and can easily come up for a number of reasons why it's worth putting up with for every reason why an impatient new player leaving a poor review might say they hate it, especially given the fact that there's nothing forcing new players to play as Sonic without Tails.