it's defo not nearly as important to focus on one character in smash bros when compared to more traditional fighting games, simply cus it's just not as complex, but maining in any game can help you better understand the character's moveset and handling on a deeper, more reflexive level. learning is about making connections, and if you spend a lot of time with one character, you make a lot more connections and learn a lot more which is useful in a wider variety of situations. in smash, a lot of the complexity comes from tiny details in attacks, movement, and damage, which you have to feel out and become comfortable with to use effectively. in other fighting games, it's typically a lot more straightforward and knowledge-based rather than felt out.