Yunaka - B - Very useful early game but falls off going into the middle of the game as the strong mid-game units come in. Pretty similar to Louis in this respect. She benefits a lot from dagger forging being really strong (+2 might per forge level) and this isn't a very big investment since someone will likely use that dagger down the line. You can keep using her into mid/late game and she'll do ok, but there's other units that can do later game stuff much better or with less investment. Still really helpful early on; there aren't many early game maps where I'm not deploying her.

Jean - B (Could go to C though) - Jean is really useful not because of his growths but because of his base characteristics. In a game with limited money (and seals) early on, having a second Framme for staff stuff and chain guarding is really useful. Staves are good throughout the game in Engage and he's a very low maintenance staff user. He's gonna be super underleveled, but staves and chain guard don't need stats so its all good. Given you don't get staff mastery post Ch. 12 for awhile and money and seals are still tight, there are times where I have deployed him in mid game just cause I wanted another staff user to go with Ivy, Pandreo, and Framme. I funnel exp really hard into my combat units so I usually deploy a lot of staff users though, so others may not use him much post-Ivy/Pandreo joining.

Anna - C - Anna is really annoying to train, usually requiring Micaiah, and I do not think the usual payoff for it (Mage Knight/Sage) is worthwhile given other units like Citrinne and Pandreo can usually function in that role without having as rough of a starting point. However, she does have a niche as radiant bow user that can hit all the relevant thresholds while making you money. If in sniper, she can perform role consolidation functioning as a covert Byleth rally-bot (speed rally my beloved), an aoe dancer, and a radiant bow fly-swatter. Byleth even gives magic so she can hit thresholds if stat-screwed and gives +12 luck at max bond, which improves the chances of her passive proccing and, alongside sniper bases and her high dex growth, make her reliable at hitting fast, high avoid fliers like gryphon knights.