I feel so much weaker now.

Hello. I'm relatively new to this game, so I'm not 100% sure about everything but it seems like since the mastery update I can't seem to build as effectively as before and I am weaker a lot longer. I tried Xin earlier today and he used to be my best Jung/Top. Now it seems like he has capped damage and cooldowns have increased. At least that is how it appears to me. I hadn't tried Ms. Fortune until after the update but I really remember her being a bigger threat than what I am doing with her. No matter what It feels like I'm really only there for support damage and using slow debuff. Even when I try to stack damage It still amounts to basically what I was doing at lvl 1 against the same person. Unless I am feeding like a shark in a pool of bleeding fish I can't seem to build enough damage to gain any real advantage against other players. The only time I have seen another player get fed enough with little farming was Yasuo and I am not sure how exactly. If anyone has any tips or input I would really appreciate it.