Man, how I love a Plant Beatdown deck. Legit, love them.
I've found Rosaria, the Fallen Angel a LOT easier to summon than I had first anticipated. With the Fallen Angel of Roses being extremely easy to summon, getting Rosaria into play is not a hassle. Summon him, use Giga Plants effect, summon Tytannial, activate Rosaria's effect if there is an opponent's monster giving me trouble, use Tytannial in case of any Solemn effects or anythign else that can blow me up, and then proceed to clear opponent's field and Life Points. Good, quick, and to the point. <3
The xyz monsters are just an additional power source, tbh. They play no real role to the deck as a whole except for helping out in a pinch.