Seriously, as much as Masuda has pissed me off with the "we're dropping Pokemon" thing, the Exp. Share is optional and not at all forced on the player. The rival having the starter weak to you is also a case of balance, as the newer starters begin with a STAB move. If you're first rival picks the one you are weak to, the first battle of the game would be unwinnable by design. You do not have the means to circumvent the advantage, so they got around it by introducing a second rival later that would have the Pokemon/type you're weak to. In X/Y, this was Serena/Calim, the actual advertised rival. In Sun/Moon, Gladion fills this position.

Go at them all day over the lack of full teams and lack of full movesets. That is inexcusable. But the Exp. Share is optional, so complaining that it exists when you don't have to use it is preposterous, and you do not have a way to work around the weakness at the beginning, so I'd rather than lead new players in with an easy fight than with one they literally cannot win.