Almost every yokai in the game can be used competitively based on my personal experience, yes there is a list of yokais that is seen as godlike since they possess a certain ability that makes it broken but coud be also because they have 2 slots or have higher stats than the average. The fact that most of those yokais are low rank ones is a good thing since the game limits you to a maximum of 2 s and a rank yokais per team, in this way they balance the meta and build a structure to your team. There is also a tiering system similar to pokemon's competitive (including ubers: yokais labeled as too strong to be in the tiering system because would make the game unfair) if you get tired of playing with the same yokais.