Bert wrote:

We see almost no real honey bees in our garden 'til late summer, early
fall when the sedum blooms, when they practically swarm.

However, we see lot of other bugs doing what appears to be exactly the
same things that the honey bees do.

Are they actually performing a useful function in the sense of
pollination, or are they just taking stuff for their own use?

Yes, hornets/wasps, etc. perform the same function as honeybees, even
hummingbirds and butterflys pollenate.