You still need to draw into Weakness Policy to not get OHKO’d, and Lysandre-ing around that is not difficult. Fighting Fury Belt is also one of the strongest cards for the deck, making the matchup against Greninja, Dark/Tina and Volcanion 50/50 or better.
The mirror-match will also be almost entirely unwinnable if others are playing FFB and you’re playing WP. Vespiquen Zebstrika also hasn’t seen that much play, and in my opinion won’t see a huge increase any time soon, because its main purpose is to beat Yveltal and Ray, but loses to so many other things in the format. If you are intent on playing Yveltal, just take the hard loss.
Also, this should definitely be in the :Yveltal thread.