No class is essential, especially a Wizard considering there are so many various consumables, scrolls and specialized arrows you can use.
With over 1200 hours here only ever playing physical classes not once did it felt like a Wizard was necessary in my party. Not even on Honour Mode which got absolutely crushed with my MC as a ranged War Cleric/Fighter, Shadowheart, Lae'zel and Karlach/Minthara. Funnily enough having a Wizard would have actually gimped my party composition because each party member has a specific role, all working together like clockwork.
Shadowheart as the group's dedicated Support/Healer (which also happens to be her canon role) will allow you to play whichever party composition you may want. But ultimately Baldur's Gate 3 isn't about what you play as, but how well you play. If you're aware of your party's strengths and weaknesses, you will have no trouble breezing through the game.
