Most people who approach ranges and dryers for the first time see 3 wires, often one is bare, and they presume "240V, 2 hots and ground". No sir. The third wire is combined neutral+ground. It's there to be neutral, and it's being overloaded to be ground, or to use the proper term, bootlegged. The appliance industry got an exception in Code notched out to make this permissible. The vast majority of dryers, ovens and ranges do use that franken-wire as a neutral. If the wire breaks, it electrifies the chassis of the appliance. Very bad design.
This was deprecated starting in the 1970s and finally outlawed in I believe 1989. Now the standard is /3 cable with separate neutral and ground. That is fine.
There's no escaping the need for neutral, eventually somewhere in a well equipped kitchen you're eventually going to have an oven, and only incandescents work for an oven light, and the obvious choice is common-as-dirt incandescent 120V bulbs, which necessitates neutral. It's common for cooktop and oven to share the same circuit.
Now it's possible you've got some ultra-modern Eurodesign that really does use only 2 hots and ground, that's particularly the case on a cooktop only that isn't an oven. Europe has only 240V, and on our side of the pond that becomes hot-hot-ground. 6/2 would suffice for that, however it would also paint you into a corner if you ever replaced the unit with another one, or shared the circuit with an oven. The vast majority still use neutral, and realistically you'd wind up horking it together with old-style bootlegged neutral-ground just to get the job done, damn the fact that it's been illegal for 30 years. Because that's the way things work in the appliance business.
In fact it wouldn't surprise me if your local inspector had a big problem with installing 6/2 and required the future-proofing of the 6/3, simply to avoid the scenario above. Same logic as needing neutral in switch loops; easy to do it now, prohibitive to do it later.