I’ve been playing around with an Arts crit team myself, recently. Maybe we can share some experience!
In my opinion, just one 2030, without some form of active stargen, is pretty sub-optimal. You either need two of them, or you need some other form of star generation to support the one you do have. Eight stars per turn is just not enough to crit consistently.
I also find that arts crit is tough to pull off with a standard arts team setup, as you’re always trying to get arts chains to generate NP, which often means needing to use sub-optimal cards from your non-DPS characters. There is this tension between focusing on your high-crit servant’s cards and charging your support servants’ NPs. This isn’t as big a deal when you’re dealing with Buster crit, as the burst damage is so high that you can afford a turn or two of lower damage arts chains, but with Arts crit, your damage is more gradual, so those low-damage turns tend to add-up and really extend the fight. This necessitates more survivability via defense buffs and healing, which usually means needing to focus more on your supports’ NPs (read: Tamamo’s NP), and… Well, you can see the problem. You often have to choose between sustain and damage.
What I have come to settle on is to focus mostly on NP-spam, but have crit damage as a secondary benefit for single-target boss killing. I use Nursery Rhyme as my DPS, as she has an AoE NP with a good chance of charge drain, helping to clear waves and delay boss NPs, while also having Self Modification, to enable strong crits when I draw a brave chain with her. I have her using Black Grail in a party with Tamamo (Prisma Cosmos) and Merlin. For Merlin’s CE, I either use Devilish Bohdisattva, if the fight won’t last more than 8 turns or so, as that allows a major head-start on stargen/NP gen and healing via Garden of Avalaon (which will produce as many stars as two 2030s by itself, for the first 5 turns). If it’s a longer fight, I will go for Prisma on him, as well, as then you can pretty reliably stack his NP.
I find that this setup has a pretty good combination of AoE damage (from Rhyme’s NP spam) stalling (from Rhyme and Tamamo’s charge drains, and Tamamo and Merlin’s heals) and burst ST DPS (via Rhyme’s crit buff and Merlin’s Hero Creation powered by his NP’s stargen).
Honestly, it’s probably not as generally effective as a more meta Tamamo/Waver/[ST arts NP] setup, but it works fine (and my Waver is bond 10, so I am trying to give other supports their time to shine).
As for your CE question, have tried Formal Craft and Another Ending, and I keep coming back to Black Grail. The Atk bonus and NP damage buff is just too strong, and I honestly don’t even notice the demerit. With all the healing available to arts teams, they usually remain at max HP unless they get seriously focused-down by some unlucky crits. Also, CEs with Arts effectiveness up don’t stack as well with Fox’s Wedding, so you’re better served with NP damage or straight attack buffs.