I don't think there is a hard level cap, specific to the demo (though the xp gain tapers off relative to your level, so it is a lot of effort with the current avilable monsters to gain level's eventually), my lvl 16 mystic have I think it is lvl 3 blink, which is pretty darn fast already
EDIT: Actually lvl 16 Mystic have rank 4 blink, with a 0.31sec cast time, and it says indeed at rank 5 that it will be instant cast). which already at rank 4 is fast enough that I can cast it between the "cooldown" between 2 dashes already