Well Disney would have access to the actual source material and better equipment, meaning that if done right, a restoration of the originals by them would easily trump anything Harmy or any other fans could do. Also there’s the fact that the Despecialized edition is, at the end of the day, nothing but an impressive fan-edit that only dedicated SW fans would even care enough to seek out in the first place. An official release would clearly give the originals more exposure. So no, I do not think Harmy’s work, as great as it is, is more important than an official re-release of the theatrical cuts.
Mind you, with all the different editions of Star Wars that are available now, I feel that the only way to truly satisfy everyone would be to remaster and release all of them with the same amount of care. I mean, I’m still pining for a high quality version of the 97 Jedi ending scene…