As you acknowledge, the branding is almost nothing to do with the publisher itself though. Nobody cares a jot that journal X is from publisher Y (I don't even know who publishes most of the big econ journals I read papers in).

The 'branding' (and I think most academics would prefer the term reputation) is developed over many years by good decisions on the part of editors and reviewers — generally academics working for free — and by others making citations. The publishers contribute negligibly to this, which is why the substantial rents they subsequently extract — and the exclusivity of knowledge this promotes — are so annoying to people.