Thing with Lyn is that she has no 1-2 range in a game where having it can make or break a unit, and Dart comes with poor bases and an effective 25k price tag.
Raigh's durability mostly comes from easy nostank, which does have some drawbacks (biggest being the price tag of doing something like that) but Hugh has really good bulk for a mage. Instapromoted, he has 30 hp and 11 defense. FYI, Lilina hits 30 hp at 20/7 and never gets 11 defense, and Lugh gets 30 hp at 20/2, and just barely misses 11 defense. Hugh also doesn't need the babying that Lilina and Lugh do, and has pretty good stats all-around. It's not hard to get him to level 20 either in 16 or halfway through 16x, (which is a lot kinder of a chapter to him then it is to Zeiss) and these five levels, along with promotion, give you a sage with 34 hp, 18-19 magic, 14-15 skill, 15 speed, 11 luck, 12 defense, and 12 res. These are very good stats for a unit that just barely joined, and his growths are decent enough that he will keep up with the rest of your army. On promo, he also gets insta aircalibur, which is pretty good in Ilia. With a speedwing, pretty much everything but the fastest nomad troopers won't double him, and with his decent durability and good 1-2 range, he can actually be pretty good in Sacae.
Raigh does have easy nostank, but isn't actually tanky without it. he has a 55% hp growth, and a 15% defense growth. Along with his poor bases in those two areas, he's not getting very tanky. Combine that with nosferatu being expensive, and there's two problems. Raigh is pretty good when used, but his bases give him some durability and combat issues (8 AS is struggling to double at this point in the game). Although Raigh does get really good when invested in, both units are with their faults.
The only other hero crest users I can think of using at this point in the game is either Fir, if you took the time to train her, or Dieck, if he managed to get enough speed levels to still be relevant.