Also incorrect. As per a CR 11 creature, it can reasonably challenge people with high degree of martial arts like Monks, Fighters and Paladins. It is able to fight through Danmaku from a Sorcerer, it is able to give a run for its money to reasonably prepared Wizards. It can fight range spam from Rangers.
All manner of abilities, specialities and combination of feats and abilities, it can challenge and win.
At these levels, a Wizard is expected to know defensive spells to counter all manner of demons, undead, fey, aberration, etc etc etc. They are expected to be fighting creatures that are quite capable of spamming stealth since even level 1. Clerics are expected to commune with their deities to gain precog and knowledge: hell, they are expected to know the lore and abilities of a Vitreous Drinker outright.
The monster can still beat them.