Straight-up aggression at best will work on low-medium level players. People without too much Fox MU experience or aren't that good anyway will cave easily into pressure because, yes, Fox is fast, but that doesn't make any of his actual attacks any safer. He has "meh" approaching options. Most characters can stuff them with their OoS options, or by baiting and punishing, etc. You can't rely on your opponent being bad for you to get better.
I still mess around with Fox occasioanlly, and IMO Fox mains should collectively look into what Fox does really well and really badly as well as his unique traits that not many others have, accept all of them, and work from there. I'm probably wrong on some things because I don't use Fox that much, only in friendlies or non-serious matches, but from what I can tell
He's really good at:
-Moving vertically. Not many other characters can control vertical momentum as well as him, because he has a fast and decently high jump, rising F-air, extremely quick fast fall, shine-stalling, and aerials that fit well with vertical movement.
-Punishing grounded lag from far away, particularly with dash U-smash
-Having safe options behind a shield
-Laser pokes
While he's bad at:
-Horizontally approaching. He has some decent approach options, but they're nothing special. Most characters can cope with them.
-Punishing horizontal approaches. Again, he has decent options, but nothing special. Most characters can get around them.
-Avoiding getting grabbed. Decent options, but again, nothing special. Repetitive yes. Things like retreating N-air or F-air work most of the time, but a lot of his things have just enough amounts of lag to them. Mess up once and you're grabbed, and things like B-air are hard to space perfectly.
-Getting a consistent kill. His kill moves themselves are good but he has some difficulty setting them up. I wouldn't say he's bad at this, he just could be better.
With this information, I personally would capitalize on a more overlooked aspect of Brawl, vertical spacing, and use his good vertical movement to see what I could do to approach or eliminate options in that aspect. Juggling, avoiding juggling, aerial approaching, etc. This with a combination of lasers means I don't have to take traditional horizontal approaches, which Fox isn't great at, nearly as much, and it will be harder for the opponent to horizontally approach me with me alternating from ground to air a lot.
Because of this, I like to play a lot of friendlies on Battlefield or other platformed stages whenever I can to try and see if the stage layout buffs my style of play. I try little gimmicky things I think of in my head and see if they can develop into something more consistent, such as full-hopping and dropping above your opponent, shining to wait for their reaction, cross-up if they shield or punish if they spotdodge or whiff an attack.
I don't know or think this is the best strategy, and I'm not saying, "EVERYONE DO THIS!!1 IT GOOD". It just makes sense in my head and it's a playstyle I want to look extensively into.