Kinda skimmed so if someone already said this oopsy. Mindflayers and other creatures used to get monster levels to show how strong they were compared to the basic races. This went with several of the races in 5e that are common now but, were actually basic creatures in previous editions. Tieflings & drow off the top of my head are good examples, they wouldn't get a class for several levels to counter how beefy the race was.
class system has always been d&d, off the top of my head world of darkness had a point buy system i think, there was also rift. That's to say were going to by pen and paper which is what d&d is based off of.
