Ending 23 years ago (and saying "12 years" is grossly overgenerous). Of zero relevance to the modern Apple computers (edit: Sorry, it isn't even called Apple Computers anymore)
His real contribution to Apple was for four years of the company's 34 year history.
If nothing else, he created the expectation that superhuman technical feats would be performed on a daily basis, which exists to this day, and might well have stayed true to some degree even during the between-Jobs years, even if said feats were not in particularly productive directions.
...during which he did things that no one else on the planet was capable of doing.