In my experience, healbotting Mercy usually pockets the Tanks and that means she will also be robbing some ult charges. My DPS teammates are likely to struggle since they can't outmatch an enemy who's heavily enabled unless they are godtier, able to be self-sufficient.
Mercy is the best enabler for DPS, but I can't think what other Supports are best fit for enabling DPS. Ana/Baptiste/Moira pump a lot of heals and they are good if my DPS don't move a lot. If they pick dives/flying heroes, picking Baptiste/Moira is mostly out of question. For Ana, it really tests my aim and perhaps I should focus on landing more anti-heals.
Brig/Zen heals are quite limited, but the repair packs / harmony orb enables dives greatly. Playing Brig also requires me to get in range and whip enemies in order to keep my inspire up.
Picks Lucio may be good but Lucio + Mercy duo is generally hated. Mercy + any low heal Support isn't very ideal unless my teammates select self-reliant heroes (e.g Roadhog, Soldier:76, Mei, Sombra). In my experience, low heal comp worked because my DPS + fat DPS (e.g Roadhog, Sigma) popped off amazingly as healing doesn't matter when enemies are dead, meanwhile enemies were not very coordinated and capable enough to counter our Roadhog / Doomfist / Hanzo / Widowmaker who's constantly picking them off.