> I wonder whether the vaccine content matters at all in current vaccines.

The target does matter, that is the basis for the whole technology, and the thing most predictive of efficacy. That's why the flu shots often don't work and the shots for smallpox and measles do, the flu is a more rapidly mutating target.

Going crazy with the adjuvants was popular during the pandemic when it became clear that the virus had mutated (the target protein), but no one wanted to do R&D for a new target. Counting white blood cells became a proxy for efficacy, and you can manipulate that stat with adjuvants.