Modern paints are water based for environmental reasons and are not nearly as durable. This applies to all makes, not just Renaults.
It's true. IIRC Porsche were one of the first to use Water based paint and got loads of stick because of poor paint quality, bad stone chipping etc.
It may be worth getting the written opinion of an independant bodyshop or paint specialist to back up your warranty claim.
Bottom line is that 'fit for purpose' must surely apply here. Unless you've used a scouring pad on the paint work you should not expect this sort of problem.
Talking of scouring pads, I once got a huge pile of bird doings on the windscreen on a Volvo, used the rough side of one of those small washing up sponges that you can buy on it and it completely scratched the windscreen to bits.