I’ve completed 7 wins on the 17 Hero Challenge, and completed every other challenge available on Stadium, so far.
Biggest difficulty was doing the 3 win Supports. Largely because… well the Builds aren’t all that great save for a specific few, and it’s a confusing mess when Ability Power and Weapon Power can both affect healing outputs depending on which healer you’re playing.
The best choices I’ve found were Moira, Lucio, Juno and Mercy. Kiriko - no matter which build I tried, pretty fell flat and just couldn’t keep up. Ana, likewise, has to split her healing focus between Weapon Power or Ability Power (pump up that Biotic Grenade healing).
Otherwise, Pulsar Torpedoes works really well when properly stacked with Ability Power, and you’re focused on healing your team with doing damage to the enemy team as a side-bonus. Doesn’t quite keep up with Moira’s healing output, but then again, very few things do.
The other big problems with Supports is not having a competent co-Support. So if you’re struggling on a build and trying to eek out value, you pretty much have to work even harder as your co-Support decides that it thinks killing targets or feeding is more fun than doing their basic job. Saw way too many Lucio’s and Juno’s propelling ahead then using their speed abilities to run even further ahead of the team.
Just grab BOB, shrink him down to size and pick up the dynamite talents for rounds 1 and 3, stack ability power and you should okay on your own. Later, if needed, you can pick up Healing BOB, or Lava Dynamites for further damage and low-ish skill damage.
If you’re good shot, you’re better off with Viper ADS stuff. But it is surprising to see how a much weaker - but much faster - BOB works on these matches.
Not going to succeed without some level of self-healing with these low-ranking/low-skilled Supports. Soldier’s great for this, Mei too. Reaper and Ashe also have some limited self-healing; but I have seen a lot of Reapers out healing Supports.
Genji requires a bit more finesse. He’s actually got fewer choices than the rest of the cast in the Damage-role, right now. Dragonblade builds work, but you need to pump up Weapon Power to really make it shine; and it still won’t last forever.