Maya is good, but needs a lot of investment, just like most heroes. Her strength is in her pure damage, which neither can be dodged or reduced by armor or magic defense, as well as magic defense from her first artifact. In addition, the amount of pure damage is amplified by Albus (overall, good pet btw) and effectively doubles it.
A few points in developing Maya:
-Maya is better with Albus patronage
-Maya is best in the 2nd or 3rd spot; her Violet ability(Queen's revenge, and the root of her high damage) activates only after the flower dies
-Maya is an all-rounder, and requires investment in all her glyphs/artifacts/level/etc. You can't go wrong with maxing out, except maybe...
-Her first skill. The lower the health of the flower, the sooner you activate the Violet skill.
To answer your follow-up question, is Maya worth one slot when you require another to have an additional healer: worth it if that healer also complements the team. For example, this team: Aurora, Maya, Jhu, Sebastian, Thea.
That team DOES need an additional healer (Thea), but she serves an additional role in speeding up Jhu. Thea's Violet skill (Second Wind) speeds up Jhu's attacks when he's low on health - this happens a lot.
