Dupreeh is ENTRY - His job is to RUN FIRST and make space. If he gets kill , thats good for the team , if not , he still push away the enemy , do some damage and gives info.
Device is AWPER and STAR PLAYER - his job is to camp ,bait and wait for other team to make mistake also sometimes he finds the entry frag. Also have much more freedom than the rest so he can run&gun if he want.
Magisk - Sometimes lurk sometimes supports dupreeh with entrying.
Xyp9x - Support player , also one of the best clutch players. (waiting for the day Xyp will be a star player and show his true potential instead of being underrated for doing his job)
Gla1ve - probably the best IGL atm , can do good damage as well unlike most igls nowadays , which use the excuse "im igl" for being bad. *caugh* Zeus *caugh*
All of them are important for the team , you overrate Device way too much. He had bad game against C9 , but magisk and Dupreeh carried him. Also rawskill Magisk > Device , Device said it himself. Device is one of the most consistent players ever , yet he chokes in most important matched.