There is an argument, of course, to be made for the reverse: the reputation a corporation can bring to the arts or social event is a plus for the local organisation rather than merely basking in the event's cachet.
Tim Horton's Summer Camps for Kids probably raises more money for the project thanks to Tim Horton's patronage than not. I dare say
Scotiabank Nuit Blanche festival, in conjunction with the City of Toronto, attracts more interest because of their reputation and sponsorship of other cultural events.
If I am hearing you correctly, you are more concerned about a corporation co-opting an already established event than starting one from scratch? Hence your example of "McDonald's Pulitzer Prize"? I would argue, if that's the case, that something like the Giller prize might simply disappear and a "naming right" which is accompanied by full-throated commitment is a small price to pay not for survival but to thrive.
(Although I have to say the shortlist for the Giller this year seems singularly bleak viewed from a number of different facets. I doubt if Scotiabank is to blame.)