Zarya is too slow. The biggest winning comps are always dive comps. Zarya is now too slow to build charge and her two second bubble just isn't enough to make it into dive, and she's got no mobility. Her ult is powerful but she never gets it built in time so it's always on the back foot AFTER a point capture that she finally gets a use on it.
Mercy is really good because her rez got really powerful, and because she's really good at supporting dive comp with guardian angel, and her 1 second cooldown self-heal. Attackers can throw themselves on the point, die, with Mercy hiding and now she can jump in and rez everyone without sacrificing herself. It's now become both one of the most powerful defensive and offensive ults.
Winston is king. 360 bubble barrier now goes on cooldown immediately, barrier-bypassing featherduster, and nerfed D.Va and disfavored Reaper and Roadhog makes him hard to kill, and the main strength of dive comps.
People just kept getting better at Tracer and Genji, and now everyone fully understanding how the both of them can kill a 200 hp hero easily in 1 second or less and have DPS to dump into tanks, defensive self-sufficiency and huge mobility, that with things like 360 winston barriers placed in their favor and everyone turned around, they're always win-win.
Soldier:76 is favored because he's just tons and tons of DPS, he's a lot faster than McCree, and his biotic field together makes him one of the best followup heroes to deal tanks like Winston and support the weird healing situation healers get in. He got buffed when D.Va was buffed, D.Va was one of the few answers, then they nerfed D.Va. Nano Boost + Visor is huge.
Reinhardt is still up there because his shield is still just so crazy strong, flickered on and off- controllable, etc. and even when people are really running dive- if the map isn't that vertical, Reinhardt getting in people's faces.
Ana is Ana, remove ult remove hero sleep dart, biotic grenade, etc.