Lists that use Shatterstorm over Vandalblast either cant hit five mana reliably, or plan on having access to four mana on turn three through a turn two ramp spell, where they can take advantage of the four CMC spell much more smoothly
Legendary cards are usually split between rare and mythic rare
Keep in mind that pack points are accumulated separately by expansion, so open booster packs from Fantastical Parade (B2) to get pack points for Galarian Zigzagoon
It's also more reasonable that you can time it to impact more games and still dodge a removal spell
Those ravinca guildmages in general were very good, and I really like rakdos guildmage, great mana sink, board control piece, and discard outlet
You should carefully consider type synergy to avoid strategic weaknesses