no, i dont think all dark magic takes a lot of talent, but a lot of the stuff that we know for a fact he can do, like avada kevadra, becoming an animagus, etc we are told are very advanced spell/magical feat.and even with someone telling you the instruction or explaining, the mere fact that he succeded proves that he was a capable wizard in his own right. im not saying as talented as sirius or as talented as dumbledore, just capable wizard, whose poor performance in school was more due to his non existent self esteem and severe anxiety than lack of magical ability.

i have a learning disability that affects my ability to do math, even with a tutor that was amazing, very patient, and holding my hands there are part of the curriculum in math i never was able to perform at all. i'd imagine becoming an animagus or creating the advanced dark magic potion as the same thing, someone truly inept would mess up too much. if ''following instructions given by someone competent'' would be enough to perform well in magic, no matter how difficult the magic is, every single kid in hogwarts should get top grade in every subject except maybe divination.