Yes, those are reference designs. Occasionally, some of those boards are a bit crappy, but generally speaking, they are designed to meet the specs claimed in datasheets.
You may wonder what the point exactly is for opamps, but if you're selecting some particular opamp based on some specific characteristic, such as very low input offset, bandwidth, or whatever, you may want to check that it'll meet your expectations, and test it in real conditions.
Making your own boards just for this is usually a complete waste of time in a professional setting. Just try and estimate the *real* cost of designing a board, even a simple one, within some company. Add up all salary costs involved. The cost of just the PCB and parts will be marginal. The overall cost will usually exceed that of a vendor-made evaluation board by a large margin.
That's actually something that may be different for hobbyists or very small companies, for which making your own boards may be worth the trouble, so that's kinda opposite of what you assumed.
There are exceptions to that - eval boards for MCUs, for instance, are often popular among hobbyists, because they are often cheap and ready to use. ("Cheap" may not be the case for "higher-end" or "niche" MCUs, for which eval boards from vendors can be very expensive, though.)