Being burst oriented, they have larger chunks of healing up front, but overall lower tails or sustained totals. Someone like Baptiste can hear a fair bit if the targets are in close for each hit or Regen Burst. But they’re all in separate directions, it’s a shot for each of them that takes more time and possibility of missing one of those shots. Baptiste can end up with high healing totals, but overall maintain a lower rate of healing per second.
Likewise, Ana’s healing is largely single target and she can area effect and boost her healing return. With proper use of Biotic Grenade and quick and accurate shots she can heal as well as Mercy. But she is also subject to missing shots or lacking the right angle, and she needs to keep Biotic Grenade usage on high to maintain it. She can outheal some supports relatively well and at greater distances than Moira or Lucio could. But she is still subject to miss rates and if Biotic Grenade isn’t used to keep health up or at pace, she can fall behind.
General rule on healing is to take the highest potential healing that any character can do in one second. Lucio, for example, heals at a rate of 16 per target, so 4 targets is 64 healing, plus himself at 10 healing for 74 healing per second. Because he doesn’t miss or can’t miss his shots, there’s little else to calculate except Amp Crossfade healing, so 50 healing per target plus 30 healing for self and it is 230 healing per second for 3 seconds.
For Mercy, she heals at a rate of 55 healing per second. There’s no chance of missing, and the ammo is not limited, so it is a constant 55 healing per second channel. In Valkyrie, this gets boosted to 60 healing per target per second, or about a 500% increase in healing output for 15 seconds. So 60 healing per target, four targets is 240 healing per second for 15 seconds. That basically beats Lucio’s highs, and can be just as frequent as Amp’ed healing.
Moira is, by far, the highest and has a limited ammo supply to balance this. At 70 healing per second per target, plus additional 35 healing over 2 seconds after, you’re looking at 280 and then 140 over 2 seconds; or 420 over 3 seconds. She has about 160 biotic healing ammo and can maintain the healing consecutively for about 13 seconds. Then she has Biotic Orb healing, on an 8 second cooldown that heals a maximum of 300 healing at a rate of 65 per second per target. Assuming four targets, everyone would get about 75 healing. This is a large improvement over 6v6 healing where she had to contend with 5 targets receiving healing at 60 per target. Moira just blows away the competition when it comes to healing. As a result, her offensive power is extremely low, and on fairly shaky ground.
There’s a lot of ignorance about whether players should be using Biotic Orb damage or Biotic Orb healing, and some ignorant players will say that it depends. It’s not really an question of “depending”, it’s a question of math. At 200 damage, against 4 targets, that’s 50 damage, or 5 targets 40 damage. This is an improvement from 6v6, but it also got hurt in the fact that armor now affects Damage Over Time effects like Biotic Orb, so there’s actually a 30% reduction in damage output against the fifth (tank) target or armor target(s), meaning that it isn’t 40 damage spread across 5 targets, but 40 and 28 damage; with more armored targets taking even further reduced damage (Fortify and other similar effects see the damages reduced even further). Either way, such minimal damage can be cleared up by any support rather quickly and it is a free 200 charge to any enemy support. That means that every enemy support is that much closer to using an ultimate to defend against another ultimate.
At any rate, excessive amounts of healing aren’t usually seen as too useful in the upper brackets because everyone there is a better shot and a better killing shot than anyone in the lower brackets. Often times in the lower brackets, players tend to die to incidental damage because their supports aren’t paying attention. While Lucio’s healing is very power, it is spread wide, and tends to keep incidental damage low or healed. More skilled players, who take positioning and communicate often and frequently tend to avoid incidental damage, so Lucio’s healing isn’t used too much except in cases where it might be needed (close-ranged brawl where speed is no longer required or needed, Crossfade over to healing and AMP to help mitigate extreme damage loss). This allows Lucio to retain high ult charge rates, high healing totals, and maximize when speed is needed. This kind of coordination doesn’t really exist on the lower brackets, so many Lucio’s should be angled towards Crossfade healing, so help with incidental damage, and stay close to the team as possible. Using Crossfade speed to chase, or escape specific dangers, or reach critical allies.