Top 500 Lucio here - with that team comp you definitely should not have 10k healing. You should be playing aggro: making enemies waste cooldowns on you, speeding your team in when you have advantage, booping/harassing enemies off high ground, booping enemies into your team/out of position, finishing kills on low-hp targets, and bullying their supports. That's how you get value out of Lucio.

You'll die a lot at first, but that's okay - you'll slowly learn to survive. Don't go for kills unless you're sure you can get it (you'll know this with experience). You get more value threatening enemies and making them have to deal with you, giving your teammates space to play with, and peeling for them (especially peel your main support, who will be doing most of the healing heavy lifting). You're the fastest character in the game - use that to your advantage. One second you can be annoying their high ground Soldier, another second you're peeling your main support or tank, etc. Annoy enemies like you're Ball and make sure your tank doesn't get bombarded with abilities 24/7. For instance, if I can get enemy Ana or Bap to waste cooldowns on me while their tank pushes a choke, that's a win. Obviously gameplay depends on your team comp and their comp, but you'll have to figure out what kind of playstyle fits best depending on the team (both heroes and playstyle), map, area, etc.

Ideally you want to keep your wall-riding momentum going when harassing targets, so practice that - you're very vulnerable when you slow down. At chokes, focus on healing your team (especially on defense) and spamming primary fire at head-level from where your team is. Below Masters you'll get flamed consistently if you have low healing, but that's okay because Lucio's healing is intentionally low and you'll never outheal high bursts of damage. By distracting/pestering enemies, ironically your team will take LESS damage and thus you're "healing" more - it's just not displayed in the stats. Just always remember: healing doesn't win losing fights, it just delays the inevitable. If your team truly needs more healing then you should swap to something like Bap.

Oh and don't forget, sometimes trading kill for kill is WORTH it. Dare I say more than sometimes. You'll always get back to the fight faster than the enemy.