Started this a long time ago, so let's do it again.
Ward hg: Seriously one of the most underrated; natural first choice for most people goes to C Wing, but this can replace Cyb Lhia in many cases (where there is already a lot of damage, and Ward hg would fit the theme).
Liam: People just remember Redra and Sasha, but Liam is probably just as good as those two, provided that Skeelz severely lack an SoA. People just build decks without him, but try to make a 3 2* deck with him if possible.
Ojibway: Somehow people just forgot about him, there was a time when he was banned every week... Still don't understand why. He is not as solid as lou, but has 2 increased damage used early, for a 10 damage that is almost irreducible.
Sayura is probably properly rated. Everytime we have a FPC discussion thread she gets mentioned, so she isn't forgotten, but having only 6 power in a clan defined by easy access to 8 power is a significant drawback.
Lorna is terrible, sorry. Copy bonus needs to be accompanied by above average (or in Skeelz's case, FAR above average) base stats. The Skeelz bonus is far, far, far, far from Saki's All Stars bonus. Lorna needed to at least be 8 power to be playable.
Ray gets overshadowed by Raven and Pilzken, both of whom have higher potential and neither of whom have a conditional ability. Even though Revenge is easy to activate, it does fail to do so occasionally, as anyone who uses Wardom or Chiara Cr knows. If Ray had an unconditional attack +8 he would be right up there with the other two.
Ok let me contribute a truly underrated character. Yet another Junkz. Kawan. Junkz doesn't have many options at 7 damage, and if Junkz has a lack of good 6 damage at 4*, how about 7 damage? Yeah, he'd be a lot better if he had protection power+damage but Junkz have other characters for that.
Lorna is great against the SOA clans, but falls short against any other card with a reducing ability. Kawan is properly rated - he's terrible in today's meta and will always be the majority of players last pick. I'd say that nearly every other 4* Junks card is better than him.
Sayura: You have a good point . However, though she is definitely not in the top meta, probably one of the sneakiest cards and she is actually fairly usable.
Lorna: You're damn right. Copy: bonus is not much needed.
Ray: He is solid, just not as good as competition. Though I am personally not a huge fan of raven (massive damage I know, but that is all he is, can't OHKO), but even then there is pilzken and naginata (YES THAT IS UNDERRATED). Right on kitsune.
Ralph: Actually not half bad of a card. Thing is a bit too much competition. Kamekun, Shifou and even bengal.
Kawan: Sorry, not kawan. 6 power is terrible for a 4*, +8 attack barely does anything. It is solid, I'd give it that. But junkz has far better options, like pretty much anyone else.
Another few underrated:
Miss Jessie: Surprisingly good in mono! I promise. Well, not top of meta card, but certainly very fun and definitely usable.
Amanie: Don't remember if I mentioned this one, but yeah. People think of tuck and gretchen, but she is completely forgotten. Tuck is very solid, but gretchen don't always fit in all decks (especially decks with natural high survivability).
First, Kawan is clearly better than Bunny or Crystal. Second, plenty of 5* 6/7 seem playable (Haze, Skyler, Havok) all of which suffer against both PR and DR. Kawan is the best 4* Junkz against SOA, and most of the 4* Junkz have circumstantial abilities. Whenever the meta is 50/50 Roots, why not Kawan?