I remember a long time ago when I wanted to pick up Marcina for tournament (my most used character by far at this point in time) I found that I was quite terrible at playing Marth and had to rely on Lucina to win. I went to the indomitable
Shaya
for advice to explain why I was so much better with Lucina.
His response was,
"Training wheels"
I found that to be very much true and as my spacing with the character got better over the 6-month period following that conversation I definitely ended up seeing more results with Marth.
If you can play Lucina, you can play Marth. There are a handful of important differences (b-air vs. f-tilt, and Lucina's f-smash baits), but the hitboxes are so similar you might as well take the time to get used to Marth.
ZeRo should try it. I'm not saying that Marth is better than Lucina because I don't want to go into that can of worms, but it's odd to say that you can play Lucina but can't play Marth. Like, what? Just put in the extra effort, you already make a living playing this game, it's
actually not like you have better things to do. You might say that you value Lucina's consistency more, but what you're obviously looking for is a way to slap someone silly with early kills like Nairo does with up-bs or Fatality does with spikes. Marth fits perfectly for that.
If you want someone who:
-is consistently strong in neutral
-has the ability to seal stocks early
-is good at ledgetrapping and following up in advantage
it honestly sounds like you're describing Marth.
or just play Rosalina