Doffy doesnt need to fly to use awakening threads though? Just see how he used Ever White against Luffy. He turned an entire town into strings and used Flap Thread.
Here waiting it out simply means Jozu has to harden himself entirely and do no damage to Doffy. And then again, why should Doffy be the aggressor here if Jozu is gonna just stay in Diamond form and do nothing? He can simply stop attacking. Also look at what happened to Luffy against Ever White, he lost his footing and was at the mercy of the threads.