Most component-level comparisons are based on spec-sheet ratings rather than direct testing. Actual reliable testing of e.g. capacitors would be another order of magnitude headache above proper testing of power supplies. Not only do you need to test larger batches to get reliable data (and data on reliability) but you need to start throwing in environmental control testing, lifecycle duration testing, etc. This sort of testing is done by the component manufacturers themselves (of their own components and of their competitors) but I am unaware of any independent bodies who test wide ranges of components, and certainly not ones who publish their results publicly. Even things like MIL-STD testing is conformity testing rather than 'quality' testing.
In my view, as long as you trust the manufacturer not to be fiddling their spec sheets (or your supplier not to be sending your knockoffs) if two components have the same specs they may as well be equivalent quality for all practical purposes. Unless you're intending to do something extreme like stick a device in an oven with no maintenance for a decade or two (at which point you have a whole bunch of other issues beyond just component selection. No good picking 'top rate' capacitors if you then use high-acid solder at too low a heat, skip pre-soak, don't wash the board, and forget the conformal coating).