Looks like I totally mis-judged this fusion - I thought I could aim to win tournaments for extra pieces so as to avoid the Summon Rush, but that's obviously just for fragment fusions.
I only have 3 sacreds and I'm in mercy territory for them, so am saving for a double legendary event as seems the most efficient way to use them.
I guess I'll just be aiming for 2 epics and 2 rares then, which should make for a stress-free event. :))