Original poster here. Adding a photo to show where marbles came to rest after being released from corner of shower floor. This is exactly where water is pooling.

Marbles at rest

Yes the floor should have an even slope to the drain- it’s kind of shower 101. Call the gc back and insist on a repair.

Bird bath and not acceptable. Redo on his dime.

Would he have to also redo the rest of the shower because of the waterproofing?

"Would he have to also redo the rest of the shower because of the waterproofing?"

No. The TCNA allows tile installation over existing tile; no endangered waterproofing by demolition.

It sounds like the marbles are defying the laws of physics. Place a long level, or a short level on a straightedge, in an "X" fashion over the floor please.

This is a good reason to use a shower pan instead of a tile floor. The shower pan is going to come with an ideally sloped basin and isn't dependent upon the skill of the installer.

You say, "But I want tile on my floor!" So get a tile-ready shower pan and have both the quality of a shower pan and the look of tile.