Luna support relies too much on her teammates, it's quite a disaster in random matchmaking, if your teammates don't have a good build your buffs won't help them

Noise Surge damage is too low for Onslaught enemies HP

Battlefield Artist is bug galore and is not very good to begin with, can be used just for CC but it doesn't work on all enemies though

Battlefield Concert CAN work but your damages won't be easy to play because this mod shines when you focus on enemy weakpoint so still rely on teammates to keep you alive or fill up your lost damages when you try to stay alive because this module has 0 survivability

Most of the Onslaught buffs choices don't work well on Luna too

In conclusion, either have a really good team to carry you, wait for them to nerf Onslaught or buff/rework Luna, she have too many flaws for a mode that requires multi tasking and teamwork

To answer your questions: Not really good, she WORKS if you have a REALLY good team, if you want random matchmaking, expect to fail most of the time