Lucina is very netplay friendly, she's the type of character i'd expect to have a high winrate online. No spacing mechanic on her sword, good punish with Fsmash, an option to break shields, a counter move, ect.
Aggressive play loses to defensive play on this game. You have to learn to be aggressive by abusing the defensive mechanics in this game. Yes, i know, "that sounds stupid" you think, but it's how this game works.
Learn the art of runup > shield. It beats like, everything.
Learn to read your opponent's airdodge habits, and learn to bait them into doing it for an attack or grab.
Also, learn to read the situations when your opponent wastes their second jump. It leaves them in a terrible position if you get them offf the stage. Combine this with airdodge reading and you can do some real damage.
Learn to respect the fact that rolling/sidestepping is stupid on this game. If you have a character with long-active hitboxes that easily punish rolls, wait for the frontroll and smash them for it. Otherwise, just learn how to let it go and go back to neutral.
Again, just because you know a roll or sidestep is coming doesn't always mean a punish is going to be easy, depending on your character. Rolls are very good, and some players, even "scrubby" ones, know how to abuse this in a way that baits you into a bad situation. Netplay just makes it worse.