Custom ring expectations

My boyfriend and I put down a $1,000 deposit for a “custom” engagement ring with a local jeweler. I’m starting to feel really discouraged with the process.

• I brought multiple inspo photos and clearly explained what I like.

• After trying on stock rings, they sent a CAD of one of their existing designs with double prongs added.

• We’ve gone back and forth ~40 times making small tweaks.

• It feels like I’m modifying a preset setting, not getting a design built around my vision.

• They only use CAD, say it can’t accurately show final proportions after polishing/engraving, and can’t render it with the elongated old mine cut center stone I want. Because they don’t have a stone like that on hand

At this point, I’m frustrated and don’t even like the ring anymore.

Are my expectations unrealistic for “custom”? Should I hire an independent designer first and then have a jeweler fabricate it?