I'm gonna try not to parrot what Azure has already covered, but I have a few extra bits to contribute.
I dunno man, we must have different definitions for what 'being aggressive' is. You can't just go in whenever you feel like it with Roy because he has no good moves on shield. None of his moves that have fast start up have fast wind down, so you can't just spam fairs like Marth can. The only good move on shield Roy has is dtilt, and that's grounded, can't be done in dash dance (without wavedashing down), is fast, but not fast enough for a rush-down strategy. Don't confuse being very good at comboing as 'I should be aggressor the whole game', you'll lose if you do.
You actually have to be extremely patient with Roy more often than not, exactly like how Cpt. Falcon does. Roy has nothing to force an opponent to come to you in the neutral, so you're more often than not dash dancing and wave dashing, just trying your best to bait them to over commit, in the neutral. And I guess this where you mean to 'be aggressive'? Once you see an opening, yes, by all means, go in, because Roy can combo very well. And on a lot of characters, his combos lead to death, so taking that opening can is crucial to winning. You gotta know when to pull the trigger, not 'be aggressive' the whole time.
And then this brings me back to the Zelda answer I gave earlier, and since you brought up Samus, I'll talk about that too. With Zelda, much like against Luigi, if you're over ambitious and try to go for long strings that would work against even characters like Sheik and Ivysaur, you have to hold back just a bit. If you try and just beat them with shear speed and accuracy in tech, it just won't work. The Zelda WILL di away, and when you go for that other fair or uair or whatever you're going for, it won't hit, and you'll take a fair/bair to the face, with a calling card saying "Thanks for doing the spacing for me, enjoy your next stock!". So in this case, not only do you have to patient in the neutral, you have to be patient while comboing too. Going for true combos will get you punished, so waiting and seeing what they do and going in after is better.
I don't know how many Samuses you've played and how good they are @
Azureflames
, but being in that range outside of a combo is extremely dangerous
Wait wait, first off, dtilt is definitely not the only good move Roy has on shield. Properly spaced, a lot of his moves are good or safe on shield, like DED, nair, ftilt, uair... Dtilt is far from alone. And that's ignoring the fact that Roy has one of the best grab games in the game, combined with a great dash dance. He also has great conversions off of grabs on Zelda.
I think you're grossly underestimating the aggressive value of dash dancing and wavedashing, but also overestimating the patience Roy needs in this MU. Dashdance grabs, spaced nairs, and even SH fairs alongside dtilt approaches can be very effective against Zelda. But DD and spaced aerials don't have to hit the opponent to be aggressive. A lot of it is about forcing them to either commit to an option or move back, which limits their options. Since Zelda is great at controlling space with Din's, this is incredibly important in the MU. Being aggressive doesn't necessarily mean going for hits, it means unrelenting pressure, and pressure is granted by
position, too.
Going for true combos will get you punished, so waiting and seeing what they do and going in after is better.
This is simply false. The definition of a true combo is that you hit them again before they exit hitstun, which means if you get knocked out of your combo, it was never a true combo in the first place. If you get hit, you overextended. Zelda isn't actually that hard for Roy to combo safely. If you space his aerials properly and use them smartly, you'll be fine. Uair strings in particular give Zelda a ton of trouble, since she has no really good way out of it. She can use her upB to return to the ground, but that's a risky and punishable option as well.
Don't believe me? Watch Sethlon vs. Grime at LTC2. Remember, this is back in 3.02 when Zelda was
better at zoning with multiple Din's, so her control of space is even better, and also when her fair and bair had super sweetspots, making them both substantially more powerful an punishing than they are in 3.5 currently.
Immediately you can see how much time he spends approaching, and is constantly pressuring, advancing, and attacking, without giving Grime any room to breathe. The first thing he does is waveland onto the platform, advancing on Zelda. Then he drops through with a fair, commanding space with the hitbox to ensure Zelda won't move forward from the edge. Then he immediately commits to a full approach with a SHFFL nair, which is spaced to hit with just the tip, so even if Grime had shielded, he wouldn't have been able to shield grab and Sethlon would have had his options open.
Throughout the set, you can see that Sethlon is approaching
much more than Grime is, and playing much more aggressively, because that's what you should do. If you put Zelda under pressure, you force her to play the game on your terms. Patience is always good, and of course you need to play smartly aggressive, but aggressiveness is still a better option in this MU.
Want evidence in 3.5? Here's Sethlon vs. Oracle in IaB34: