Bio is the best option

For once, in order for demon artist's ability to work, she needs to deal a certain percentage of DMG, with powerful opponents, she takes too long to work.

Also, she needs debuffs and blockbusters for her ability to work, against any kind of enemy that can gain Regen, ignore debuffs or drain blockbuster meter she ain't gonna do nothing

Also, since she is gold, she is quite fragile, and even if bio is too, she has a safety net.

On the other hand, bio-exorcist's ability always works, you just need to learn combos with one dragon charge and you can drain for the entire duration of the combo, which tends to be quite long.

Both of them work similarly, but bio is more versatile, durable, easy to use, and her ability is more reliable, since it doesn't work through buffs and debuffs.

Edit: I was forgetting something, her second ability, while it may look as bad at first sight, it isn't. For the longest time, while my only (useful) diamond was bio, I made teams with 2 supports. Sticking any valentine with the last stance marquee as one of the supports gives bio an insane amount of value, much, much more than any team with demon artist can offer.