Corner stones without water drainage

Hello,
My landscape gardener wants to install 50cm angle stones on the slope (50cm x 30m). Although we have heavy clay soil, he only wants to place them on gravel. We have no way to drain the stagnant water (the garden slopes down towards the planned angle stones) but can only let it seep away. My question: Won't he be building a retaining wall with the angle stones? The company El does specify that drainage should be installed in the L so that no water collects behind the wall.
Wouldn't it be better to choose a more permeable solution?
What alternatives are there?

every 50cm is indeed a drainage...

No. There is no drainage on the slope. The stones are placed perfectly stone to stone and the joints are to be compacted.

Google image search, "Drainage retaining wall", yields many pictures illustrating how to do it "correctly": seepage wall and drainage pipe. However, the water must still be diverted somewhere, e.g. seepage shaft, sump, or wastewater. But with a garden wall, the world will not end if you skip that – founding on 30 cm of gravel and backfilling with gravel also provides some drainage.

But I suppose I will get a damp corner with my clay floor, since the water will accumulate behind the stone. Or?

every 50cm is a drainage...

I agree. As long as the joints between the L-shaped stones are not somehow waterproof sealed, water will still get through there.