The 30-year-old escaped from the remnants of a breakaway to claim his career first Tour stage triumph following a title bid at the Giro he finished seventh overall at this year.
Mollema in a post-race press conference joined a growing chorus of industry insiders that have dismissed the tightly-timed double as a realistic objective and cited Nairo Quintana (Movistar) as evidence.
Quintana at the beginning of the season outlined his aim to win both the Giro and the Tour. The Colombian finished second overall in Italy behind Tom Dumoulin (Sunweb) and estimated that he would be even stronger for July.
He showed glimpses of both form and fatigue in the opening two weeks here but hemorrhaged time in stage 15, which he finished more than 10 minutes in arrears of Mollema and plummeted from eighth to 11th on the general classification - now more than six minutes behind yellow jersey and defending champion Chris Froome (Sky).
There is sentiment his fall will discourage anyone else from attempting the double for some time.
Mollema a veteran Grand Tour rider, with 10 finishes to his name, also rode the 2017 Giro, finishing 7th overall.
He has backed up well at the Tour, though with a different set of objectives, and is 24th overall at 34min 50sec behind Froome.
“I think after the Giro it’s too hard to also do GC in the Tour,” Mollema said. “That’s what we saw I think today with Quintana losing a lot of time again, so that’s a really difficult combination.
“But to do two Grand Tours a year - one of them fighting for GC and maybe the other one going for stages - I think that’s something I would like to do in the next couple of years.”
Mollema had been working for Trek-Segafredo teammate Alberto Contador at the Tour before the squad revised its aims when it became clear a podium with the Spaniard was out of reach.
"I really like to fight for the general classifications and normally next year I will go back for the Tour to fight for GC. That’s what I really like as a rider, is to fight three weeks in a row and give everything every day," Mollema said.
Orica-Scott sports director Matt White, who is governing three burgeoning Grand Tour leaders in Esteban Chaves, Simon and Adam Yates, backed Mollema’s sentiment on the double.
“I think you can do it successfully, but not for GC,” White said. “I think older guys can use the Giro to prepare for the Tour, you can win a stage in the Giro, like [Sky’s Mikel] Landa is doing, but I think to ride the Giro and Tour for the win is impossible.”
Landa entered the Giro as a co-leader at Sky. He fell short finishing 17th overall but took a stage victory and the King of the Mountain as consolation. The Spaniard has been notably strong at the Tour, supporting Froome and also sixth on the general classification.
The title double hasn't been achieved since 1998. Quintana adds his name to an illustrious list, including Contador, that have tried and failed.