The way the meta should go

Assassins should be beating mages and marksman. Eliminating big threats and getting out relatively safely if the team is not paying attention. However they should lose to bruisers and tanks, being unable to kill them with there full burst unless very far ahead.

Mages should outrage and defeat marksman while being able to kite bruisers until they die. They should lose to tanks, who can live through the spell rotation and assassins who burst them down.

Marksman should defeat tanks by there sheer dps and armor pen, and also defeating bruisers by kiting. They should however lose to assassins because of there burst against squishy's and also lose to mages because of outranged damage.

Bruisers lose to mages and marksman as stated above and defeat tanks and assassins by being able to tank there hits and still output significant damage

Finally tanks should beat assassins and mages by living through there spell rotation and dealing enough damage to destroy there squishy selves, while losing to bruisers who can put out enough dps to break through there tanky shells :)

Good luck on the rift,

fetch