Level-three headers (===) are well established as the standard header on Wikipedia. If you hate this so much, better to simply redefine it to pump out ideologically correct H2 tags instead of H3 rather than to prescribe the change of thousands of pages and demand a change in markup behavior.
I don't think it's "well established" at all. I always use == for my first subheads, and many others do as well. There's a nice simple correspondence between ==/H2, ===/H3, etc. H1 is reserved for the article title. If we shifted === to produce H2 as you suggest, then what whould == produce?
I have heard complaints that people think H2 is rendered too large; that can be fixed with stylesheet changes, and I'm certainly open to doing that. But let's settle on a standard for reasons other than mere inertia.