Ideally we shouldn't need a mod to begin with, but it is always a fallback option if some kind soul out there with enough time on their hands decides on that undertaking.
I would really rather the core game was right, considering it may well be built on for future releases (DLCs, spinoffs, sequels). We shouldn’t need mods for all of those too. Besides, the more Larian improvise, the more work they’re making for themselves trying to balance things later on (assuming they care about balance). I wish they would trust the rules. Flaming Sphere is just the latest example of how they’re trying to shoehorn D&D into their mechanics rather than build systems to make it work that will useful for other spells. I think we can extrapolate that Spiritual Weapon is going to be just as mangled.
Going so far off-piste is really going to hurt if Larian does end up pursuing a DM mode. Having a really strong foundation that could be used for people to build modules and run games like a VTT would be incredible, especially for folks who can’t play D&D in the same room. But that won’t work if the ruleset is some kind of bastardised offshoot that will only get more hackneyed as more subclasses, spells etc are added in from other sourcebooks.
Perhaps I’m better off placing my hope in the Solasta team, maybe if the game does well enough they’ll have the resources to work in that direction.