Nostalgia is literally the
only thing AD&D has going for it - it's a clunky, incoherent, and thoroughly unbalanced mess, designed when tabletop gaming was only a decade or two old.
We've had 35 years of experience with tabletop and CRPGs since then, both with systems that tried to stick closer to D&D and with ones that tried new things altogether.
The Divinity system isn't perfect by any means, but I can't imagine how rose-tinted your glasses must be to think that THAC0 and the golden age of Linear Fighter, Quadratic Wizard are better.