Also, I'll answer your post in the video thread tomorrow, I have to go for tonight. The short of it is that you had a better concept of stage control in that one, compared to your tournament ones. Keep center stage as much as possible and don't try to attack when you don't have frame advantage(like when you are next to their shield).
As I said before, if this is from frustration or disappointment, it will subside eventually. But if you are feeling like competition is too toxic for you and makes you feel bad all the time, maybe consider playing casually from now on. Again, don't keep playing out of some sense of not "running away." There will be other things you might end up actually enjoying that are more worthy to invest your time and energy in. If you don't know what they are yet, maybe take a break from Smash and go try other things that interest you. Competition isn't for everyone nor is competitive fighting games. Don't forget you can always come back to Smash if you feel like doing so.
Or Ultimate might not be your cup of tea either. Maybe try playing other Smash games again or just other games period.