Not the next instant or sorcery spell, the next spell
My commander of choice was Golos, Tireless Pilgrim and then I switched it to Sisay, Weatherlight Captain when Golos got banned
3 Reanimator Reanimator is another fairly straightforward deck, though it involves some planning to get it right
However, its real strength is the fact that whenever you cast or copy an instant or a sorcery spell, you get to create a Treasure token, which you can sacrifice for any colour of mana you want, whenever you want
As for playing with Wilhelt in the wider format, I think its actually a really great option for Zombie decks, especially seeing as though you can lose a whole board of Zombies and get an immediate replacement board of decayed Zombie tokens
Sanctifier of Souls 3W Creature Human Cleric 2/3 Whenever another creature enters the battlefield under your control, Sanctifier of Souls gets +1/+1 until end of turn