Yeah that's probably why your attack is so low.
Not many users need the healing. especially if you put a healer on your team
such as Bennett, Barbara, etc.

Most need different things. Only healers need HP and healing bonuses.
More characters usually need atk % crit dmg, crit rate and energy recharge.
Sometimes elementary mastery. Mostly elementary mastery i put on Pyro and Anemo characters.

still that's probably why your characters are
not doing the dmg they are doing from all the HP/healing they have
as with artifacts they don't really do much for those who don't really need it XD

i keep Noelle as my healer because she is a dmg healer.

Noelle deals dmg when she has her shield up, and as she deals dmg
she heals. As she is my main healer i use.
and her artifacts you mostly just need HP, DEF, ATK % and probably energy recharge since it's a pain to get her burst back.
But she is a great healer in my opinion.

I never take Noelle out. when i do...oh boy...a mess.

Basic noelle should. i don't think you need constellations for her healing abilities
since when i first had c0 of her i never noticed she needed constellations for her healing. You just have to deal damage to get the healing. it's not a huge healing bonus. Bennett or Sayu or even Jean usually heals if you stand in their circle and it's like 1-2k HP they heal quickly.

Noelle is more gradual. it's every hit you deal. but it's usually around 500-700 HP
depending on artifacts i believe.
But she is very useful. Her shield is not the best but it's better than nothing.
tho her shield tends to wear down once it gets to 12-14 seconds.

Most say Sayu is not very good. but i only have her at 50 so i can't really test out why. I want to do a litle test with every healer that has a circle to see who heals best. but Bennett is very good as he also boosts abilities.
tho i need to level my jean since now she is c1.

I def recommend Noelle.
Many of my friends don't like her much but i feel you really need
to know how to use a character before fully saying you don't like their play style.
tho I have been playing with Noelle since i began playing a year or so ago.
so I can definitely say she is very useful.

Mine isn't quite leveled just yet, but i am working on building her better.

Sayu I mostly just want as a healer. i don't like her rolling around. It's quite annoying to me lol. so i don't use her very often.
mostly i use her to catch crystalflies as well.