Portland cement neat is waterproof. I have a 3000 gallon above ground cistern that does not leak weep, or get damp. the inside and outside are painted with a heavy coat of pure Portland mixed with a small amount of sharp sand to increase coating thickness and give tooth to any needed subsequent coats.
If it was me, I'd paint the floor with a heavy coat of pure Portland and a little sand, then while wet, put down reinforcing steel mesh and add another 4" of very rich concrete over. I'd skip membranes, as yes, you'll get no bond at all , and it's just wasted plastic technology BS. You'll just have a layer of water between. Raising the floor 4" will help with drainage, too.
4" minimum over and yes, reinforcing, so nothing moves or cracks ever again. When semi cured, I'd hit the top surface with one more coat of Portland and sand. This whole will be waterproof.
Drainage won't stop a permeable pad with water under. You want impermeable, and made out of like materials. Forget plastic miracles. Sure, improve drainage, but a spongy concrete slab is just that, a sponge.