Deschamps rates Dembélé since he made him start multiple games, including the first one at the World Cup. Now Giroud just has a different profile that matches pretty well with the rest of the team. But Dembélé is supposed to be the one who takes Giroud's spot in the years to come.
That, and Dembélé is still a bit shy in his game compared to Mbappé, nobody denies that. Mbappé is more mature and less likely to lose the ball. Which doesn't mean Dembélé has an inferior potential. He just has to be trusted and get as much game time in club as Mbappé.
And no, the board didn't try to sell him, since it would hardly make sense spending such a huge sum then take a loss after a single promising season and 2 injuries. That's the not the way clubs are managed.
The sum Barcelona spent on Dembélé means they think he's basically the best young player in the world along with Mbappé. They won't give up after one year and take a loss.