El Presidente is made with blanc vermouth, not dry. The extra sweetness complements the small amount of grenadine and curaçao. Why fiddle with what is already a nearly perfect cocktail?
It doesnt matter wich vermouth you use in the end you can balance with curacao grenadine lime or sugar. In fact the rum you use will change the flavor, so its personal taste.
With only bianco vermouth the Presidente needs a splash of lime [see “El Presidente (Sloppy Joes)” link above] or it is too sweet. However, I also see that with dry vermouth some find this too dry. Hence, in the spirit of compromise, I’ve moved to 50:50 of each vermouth and must admit that the cocktail is better for it.