Let’s face it, the carpet mats come, packed in plastic bags, in every GTI, ready to be fitted by the dealer at the PDI. They’ve either been mislaid, or nicked. The salesman is trying it on with you - I simply can’t believe he doesn’t know they should be there. As you can see from the chart above, its only the Lite that doesn’t get them and I’d bet they sell more GTIs than Lites!
There’s no argument really - the sales literature says it all.
EDIT: Re read OP and realised that your car hasn’t arrived yet, so I’m talking rubbish, as usual. Still think it very unlikely that carpet mats would be deleted from the GTI spec. The Configurator shows the same as literature above, with just the Lite doing without.
In the (very) unlikely event of the car turning up without, better ones are available after market, or oem on eBay etc, or you could have a double or quits bet, with the salesman, that the car comes with them!