I think anything faster than 240/250 bpm for a kantan MUST have lower slider velocity, for futsuu there could be some arguing but kantans are supposed to introduce players to the game. How can you be introduced to the game when there are notes flying by faster than even some more experienced players can read? It just doesn't make sense. A lot of the time I see people simply shrug off guidelines without exhaustive reasoning. I think to have it truly be always enforced in kantans it needs to be a rule. Also if the futsuu is the lowest diff in the set I think it should also have a similar rule.