These are useful and well made, thanks man.
I almost entirely play Lucio so I thought I'd chime in what I've learned with him so far.
He does seem to be useful with basically anyone and anything, if your team insists on playing a thousand snipers in a thousand different windows and ledges then its less effective but still.
He is amazing at holding objectives especially the payloads, seriously. I land Gold objective time with this guy almost every game, if you have a good tank beside you then even better. Holding the payloads is what he seems to excel at though for sure.
For his weaknesses, Roadhog is arguable. He can definitely insta kill you with the hook but that rarely happens to me, I'm not sure if its lag? but 95% of the time I just do the knockback the moment I am out of the hook animation and it keeps me comfortably alive. His ulti can be nasty too but easy enough to avoid.
Widowmaker is also somewhat debatable, if its a really good Widow then yes absolutely because she can 1 shot you. However I also do a lot of counter-widow playing, Lucio's gun is perfectly accurate and the delayed shot is surprisingly good at catching snipers when they re-peek you. Doing that whilst staying as mobile as possible can usually at least force them to take cover, reposition or waste time looking to heal. This is all also true of Hanzo, though he has a much harder time hitting you if you are very mobile.
Pharah is 100% true, its nigh impossible to hit her whilst she's flying around with Lucio's gun because of the slow moving shots. You can when she is stationary during her ult but if she's doing that you want to be hiding instead. This is easily the hero I am always the most useless against.
Tracer is also mostly true, again its dependant on them being a good tracer. A lot of the time I just go against the extremely blink happy ones that zip in, nibble at you a bit then run away which just makes them useless. A good tracer though can very easily hound you to death. Definitely be careful around these, but as Lucio you should never be on your own anyway.
He is surprisingly good at dealing damage to most dps heroes, particularly the ones who like to be stationary. Like I mentioned with Widow, even if you don't kill them you at least force them to get up and move to reposition or heal making them waste time. It stops them having free reign over your team.
One of the most important things with him though is his durability and mobility. He is excellent at surviving for long periods of time. If you stay extremely mobile and use all possible cover to your advantage you are a nightmare to kill. Switching to the speed aura in crucial moments can help you outrun certain things too, like a Genji ult.
His knockback is golden too. First of all it allows you to get gravity kills which is not only awesome but also so good for winning a team fight. Though even when that isn't an option it just allows you to screw with people. To shove them around, stop them from getting in our out of a doorway, push them away from you (MEI) so they cant hurt you as much, (MEI) or freeze you like MEI.
He is by far in a way my favourite hero in this game, to me he feels like the hero with the most positives and the least negatives. I'm sure some will disagree but that's my experience thus far. He's a great nuisance hero, with the ability to deal fairly surprising damage especially to long range stationary heroes, and the amazing amount of durability he brings to himself and the team. Even capable of nullifying some team-wipe ultimate's with his own if timed correctly (or sometimes with luck).
I would go so far as to argue he is actually the best hero in the game.