I think Sonic is good for 1 vs 1 battles. But sonic is horrible in FFA and Team battles with team attack on. Cause as sonic your everywhere on the field, you wont be able to spindash or spin charge in a FFA or team battle because everything would out prioritize those spins. And you would mess up your partner from spin dashing into them on accident.
But a great reason to use Sonic as your main is because...
Since you have to control Sonic's immense speed. Your hit and run strategies become alot better with other characters you use as well. And its easier to control your other secondary characters speed and dashes, since you have to get used to Sonic's insanely fast run.
And Sonic is all about mindgames. I suggest any new players, casual players, or bad players learn another character with KO power that you can spam. If you want to get good with Sonic, you'll have to actually study about the character.
![Sonic :sonic: :sonic:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)