They're very solid, but they're just unpopular. In my case I don't use them much because they're fairly weak in halfs. Of course, then the downside of mono is that you will have a bonus that does nothing the majority of the time. They're situational, and on strong SoA weeks like this(Rolph unbanned) you'll see them at higher elo.
A few reason:
1. They aren't overly great in a half deck (splash is good though) meaning they're more effective in mono
2. They lack a powerful nuke that most other clans have, even their 5* cards that are actually useable lack damage
3. The 5* that are actually good either have weird abilities for their star count (Such as defeat) or simply lack damage (Minerva)
4. Their 4* are lacklustre with only Dr Falkenstein being a 'great' card.
ie: Upper half of star count is very weak/ doesn't support the clans needs
Aylen is a monster of a card, so under rated, dr falkenstein, kent, sasha, lorna are all tanks and provide you with the attack manip to take on all the attack manip clans, and when not facing them, destroying the non attack manip clans, and sandro's 10 power? Yes please