When Levine states that "Pizza sauce should not be slow cooked", he is probably referring to the traditional "Sunday gravy" in which the sauce, usually combined with various meats, is slow cooked for several hours.
That being said, while I usually use an uncooked, lightly-seasoned sauce on my pizza, I've lately been making pies, with leftover Sunday gravy simmered with sausages, that have been excellent.
Now, I've made pies in the past with long-simmered sauce that have been pretty bad. This sauce was made with top-quality Stanislaus tomatoes, was still fairly thin, and was applied very lightly. That combination, I think, allowed me to get away with it.
Ideally, I think an uncooked sauce is the ticket, but if you don't want to open up a can of tomatoes for one pie, or have some leftovers you need to use up, thinning out the sauce and using just a small amount will do very nicely.