According to Kuroganehammer's website (frame data for smash 4) I see a consistent trend. Lucina's aerials have at most 1.6% less damage than Marth's tippers. Fair and Bair have either 1% or .7% less respectively. UpAir has 1.6% less, and Dair has 1.7% less. Nair1 has .8% less, and Nair2 has 1% less.
The most commonly used aerials? Fair and Bair for myself, with Upair being next, and I personally rarely use Dair in a serious match.
Ground moves?
Marth advantages in % with a tipper:
Jab1: 1.615%
Jab 2: 1.25%
Dash atk: 1.015%
Ftilt: 1.075%
etc
Lucina damage advantage compared to non tippers:
Jab1: +.325%
Jab2: +.75%
Dash atk: +.975%
Ftilt: +1.925%
etc you can look these up yourselves.
When you look at the numbers Kurogane has recorded, it's hard to make a case that tippers matter over the course of a match. When not hitting the tip, Marth is outdamaged by lucina 100% of the time in every case I've seen listed here, even if only by a little. The damge the two characters deal when played properly would seem to be about equal if marth can land about 50% tippers. I personally think that Marth and Lucina are far too similar to be put anywhere on a tierlist besides side-by-side. They are practically equal in all aspects except damage at different ranges, and even with this difference, Lucina will outdamage marth unless he can land at least 50% of tippered moves to approximately equate Lucina's damage. Marth kills earlier with tippers, he struggles to kill late because of his soft hits. Lucina can't kill with fmash before ~70%, but her Fsmash is still absurdly powerful as-is, and is not made less amazing by the potential of a tippered one on marth. These characters seem to me to be as close in power as Pit/Dark pit, who are nearly universally regarded as the same character. With only a few differences in terms of nuanced effects, Marth and Lucina are two sides of the same coin.
If I had to rank their standing on a tier list, I'd put them at outside of the top 20, but at least higher than the bottom 26. Essentially, dead middle of the pack. I'd say they are only clearly outclassed by Cloud, Sheik, Rosa, Fox, Ryu, Mario, Diddy, Sonic, Bayonetta, Corrin, ZSS, Villager, Pikachu, Mewtwo, and Meta Knight. After those, I'd say they are on par with Mega Man, Yoshi, Cap Falcon, Ness, Wario, Toon Link, ROB, Pit/Dark Pit, Greninja, Shulk, Link, and Luigi.
This is from my personal experience in the matchup between Marth/Lucina and the characters mentioned. I believe that any character I haven't mentioned is a weaker character than Marth/Lucina, or that the matchup of Marth/Lucina is favored when against said characters.
What do you guys think? Does that sound about right? Or do Marth and Lucina somehow have less usability and worse matchups than the likes of WiiFit and Lucas?