Genuinely surprised at some of the takes here! I'd like to share my experiences with Laipis and friends. First time playthrough, maddening, on chapter 12 currently. My favorite units in Fire Emblem are myrmidons, especially female swordfighters, so when I saw Lapis I was like awesome, a swordfighter ready to be promoted.
Here's the thing: she's basically a Marisa, Fir, or FE9!Mia; not an Ayra. She's got the classic drawbacks of low bulk and low offense, offset somewhat by very high speed. I promoted her immediately and got her to around level 5/6 by the end of chapter 11. She is only performing okay. I don't see where she, from the get go, clears through hordes of enemies. What does she 1 round? Mages? Pegs? Archers? The frailest classes that literally anyone can 1 round? And this isn't even 100% of the time due to her low strength.
End of chapter 11, I'm given Kagetsu. Holy shit. He is SO much better in EVERY category, if I recall. As a lower level swordmaster than Lapis (though I think his internal level of 15 would about match my Lapis at this point), he makes me feel I wasted time feeding Lapis any experience at all. He joins as better Lapis, and with a slightly better personal. There is, as of now, for a person who used Lapis quite a bit, and intentionally trained her, ZERO reason to take Lapis over Kagetsu for 1 of my 10 deployment slots.
All that said, I gave her a forged steel sword with the +40 avoid engraving, and she soloed the left half of the map with Rosado. Unreliably so, as enemy hit rates had to be >0 on her, so if she got hit by Rosado and a mook she died, which happened more often than one would think. Thing is, couldn't anyone do this? Yunaka sitting on the same avoid tile Lapis used could probabaly have done so without needing the engraved sword even, and she wouldn't need to move off the tile to attack the 1-2 range wyverns as Lapis did.
Chloe was amazing from the moment you get her. Similar combat (better due to 1-2 range IMO) but flight being invaluable for clearing paths of mages and killing the thief/mage cannon guy in chapter 10, for example. She, without trying, was promoted by the Lapis chapter. As a level 1 wyvern the comparison is not there. She entirely outclasses Lapis here.
Note that I am NOT playing efficiently. I took like 8+ turns for chapter 11, as I wanted to kill as many units as possible. Even with this slow paced playstyle, Lapis is only okay in my opinion. I feel she would be even worse in an efficient playthrough. The only counters to this I have read are anecdotes of people saying she is good from turn 1, but I have not seen any numbers to back this up, no key enemy types she is taking down, no performance indicators at all. I will continue to use her till endgame, cause she's a cute swordmaster, but when I saw most people put her in D tier, I find it hard to argue. Personally I would say C is as high as she should go, but I haven't finished the game yet so that may change.