In practice, I've found SSB too laggy to act as a camping projectile or one that forces engagements. Instead, I think it functions in neutral solely as a deterrent to camping, and sometimes hitting at long ranges if they're caught off-guard. For example, it's effective against Link and Duck Hunt to prevent their camping setups. But it's not complex enough of a projectile and has too high a cooldown to use in that mid-range (just inside Luma Warp range) where Diddy can play patiently. Think Brawl Zelda. Din's doesn't force approaches. It just forces you to play closer.
I see what you mean, and I agree to an extent about the advantages of sticking to one character, but I think there are a few characters with similar-ish (there's nothing truly similar to playing Rosalina) playstyles in terms of patient zoning that do better in some troubled matchups. I've recently picked up Mega Man and still have my Brawl Olimar instincts. Just to name a few similarities:
- Olimar pikmin priority is similar to Luma priority, and you work around its faults in the same way- being careful about clanking with attacks and choosing options that don't leave you open if they clash with pikmin/Luma.
- With both Mega Man and Rosalina, you primarily use jab and n-air for zoning/spacing respectively in neutral (cool huh?). Both jabs have some similarities that make the transition relatively easy: long range, both great in neutral at close/mid-range, they have similar frame data when it comes to players jumping OoS into aerials or rolling behind as punishment options. As for n-air, with both characters you retreat with some of them, and land close to their shield with others. Jabbing after n-airs works effectively with both characters to prevent some OoS punishment options.
A few minor similarities that form good defensive habits that transition well between characters:
- Both Mega Man and Olimar help sharpen your rolling habits, because like Rosalina, their boxing games aren't the best.
- Both characters have default recoveries without hitboxes. If you use Rosalina's custom up-b that travels very quickly, you'll have experience teching stage spikes in the same way you do with Olimar/Mega Man default up-b. (I've recently been favoring the other two Mega Man up-bs though.)
- None of them have quick aerial options to force aerial trades in sticky situations.
For matchups, I currently think both Mega Man and Olimar do much better against Diddy. I think Mega man does better vs Captain Falcon. They both generally do well against campers if you prefer not to play Rosalina for those matchups. I think with Shadow Blade Mega Man might beat Rosalina, so you potentially have that for dittos. I haven't played the matchup much yet, but I speculate Mega Man shuts down Peach pretty hard by keeping her grounded with lemon spam- could be wrong about that one.