Like a lot of spells matter creatures, Sevinne is small but mighty: he protects himself in combat and allows you to copy instants and sorceries that you cast from your graveyard
My way of thinking is that Talrand, Sky Summoner always does work in a deck like this, but Impact Tremors, Witty Roastmaster, and Purphoros, God of the Forge only do work if you have another token-making creature out, and that just seems too fiddly and fragile
It's also just a great decision by the Lorcana team as Stitch is more popular than ever these days with his box-office smash hit live-action film and a sequel on the way
To put it into perspective, a 1/1 deathtouch creature can handle it because The Tarrasque doesnt even have trample
The Disney Lorcana Experience: Disney Lorcana is not just a game
For the most part, these sieges basically replace themselves when they enter the battlefield, either by putting a new card in the players hand or creating an extra permanent in play