Hanma while i agree with that different unique kits for each characters is a good thing, the classees at this point are pretty irrelevant.
For example, Raze and Phoenix are the 'duelists' class and they aren't at all similar. Phoenix has flash bangs, fire wall, fire toss and his ult is a duplicate of himself. while raze is nothing but explosives. bomb buddy, grenades, c4 pack and a rocket launcher.
Or there are your examples; Sage and Cypher are Sentinels. they are the same class yet neither really share any similarities. Chyper is very scoutish with cameras, trip wires and his ult that spots everyone while Sage heals, slows areas, walls areas off and rezs people. if you were to look at those 2 kits most people wouldnt think they were the same class.
at this point i think the only reason the 'class' system is around is to give a loose reference of how the characters were designed to be played. what the designers had in mind, sorta speak. thing is, the abilities are very versatile.
i use sage walls to block windows and allow me to move up close unseen with a shotty. it can be really effective offensively despite what the class description might say.