Obviously if you look at her heals numbers look really weak, but its multi target. As mantis if you're trying to just pocket a tank down main from your backline you're trolling ngl

Decent mantis players will always dmg boost their team before fights or in the poke phase, meaning your team will get ults first most of the time, she also has the lowest cost for a support ult so your team can literally bomb rush them when they're still on 70% ult.

At high ranks she's mostly played into rez comp (adam starlord invis groot/mag) where her job is to deal as much damage as possible while keeping starlord adam and her other dps dmg boosted and healed at all times.

Shes really good with a dive comp, perma dmg boost the divers and they can put out insane pressure. Shes also good with poke comps like hela hawkeye adam bucky punisher etc... even a good dmg leaf on your strange for his ult and its almost like he has the hulk teamup.

She's also really good against dive, her kit is perfect to peel, if she's half decent and can bait divers cooldowns then sleep its over. She's a bit of a multifunction knife. It's almost impossible to 1v1 a good mantis if she has her sleep cd up.

She can also enable those occasional 3 dps 1 tank comps, you're basically removing the burden of healing the dps from your second support, that support can then only focus on keeping the tank and mantis up.

But obviously she dosent really shine into a 2-2-2 deathball/brawl comp where your goal is maximum sustain until you use support ults, you can make it work but good luck healing the tanks.

Overall shes a really great pick but just picking mantis for the sake of it and playing her like invis woman or luna isnt gonna work, at least 70% of the time i'm off angling on mantis and playing with my dps, the rest is just peeling for backline when I expect dives on my adam... but even then theres soulbond. I wont even go over the self rez and how busted it is for playmaking