Prepare the base for paving the driveway

I have read about 20 books and in those about 15 different recommendations for the subbase. That makes sense, because not every region has a gravel pit every 10km. Basically, gravel is better than sandy gravel and somewhat larger grains are better than the smaller ones (sand). Also, paving is not done suspended but on a natural ground, which also has a very large influence on the suitable base layer. You say you are renewing the driveway, so cars have already driven over it for 30 years? It will probably hold in the future as well, even if it's not according to the textbook.

The other aspect is the matter of warranty. Ultimately, the garden landscaper decides that. If they want a different subbase, you will need a different subbase or they won't do it.

And if he says the ground is not load-bearing, then make the ground load-bearing according to the specifications of the garden and landscape gardener

That is the decisive factor, you specify the future load and use, there are already differences between baby carriages, cars with maneuvering area, tradesmen's vans, moving vans, and tankers, let the garden and landscape gardener decide how to carry it out, he will be annoyed afterwards if the driving track subsides

Can work, but doesn't have to...

depends on the installation thickness of the material and the substrate. If you really want to keep the material in, then compact it and do a plate load test. A drop plate should be sufficient. An EVd < 40 MN should be achieved at least.

The question is whether the risk is worth the effort and it still doesn’t work in the end.

At least you can suggest that to the garden landscaper.

Regards