That said, espresso is a highly desirable form of coffee for many people. Also, any pro barista will tell you that espresso is NOT actually better with "single-source" beans. It practically requires a blend to get the best flavor profile.
Pour-over is probably the best way to taste single-source beans-- if you're interested in distinguishing the "terroir" (to borrow the term from the wine tasters).
As a former barista (incl competing) and commercial roaster, "coffee bon vivant", I agree with you (it's a rare pleasant surprise that a single origin really works out of a commercial espresso machine, IMO), but there are lots of reputable shops/baristas that will beg to differ. The whole universe/culture is big enough though that after my ~20+ years in so far I'm still open to being surprised.
I usually describe espresso coffee (the beans) thusly (crude, but effective(ish)):
The opposite of scotch - the highly regarded scotches are single
malts, and you don't want to distract from their quality. Blended
scotches are concocted to fill voids or weaknesses in in the
collection of ingredients that won't stand alone. In espresso,
there is no single bean that will provide the body, acid, flavour
that makes the best espressos, so you necessarily blend to collect
the profiles you want into a single product (the coffee blend
you'll use). Some even use beans that (in N. America, at least)
we're advertised-to are inferior (robusta[0]), but even these
have desirable properties[1], in the right hands.
Edit: clarifying words, formatting
I might have been more apt to at least lean in this direction a few years ago, but now I just disagree. It's like saying that a Ferrari is the ultimate form of an automobile. That's not true if your test is navigating the Rubicon Trail[0].
Very rarely (1 in (maybe) 20) do I have a single origin[1] espresso that isn't disappointing (that's not 1/20 shots, but 1/20 different single origins, from different roasters, from various shops).
Enter the pour over[2]. A Chemex[3], Hario V60 dripper[4] or similar and a good Ethiopian or Kenyan makes absolute candy in my cup. The pourover is what introduced me to what a single-origin bean can be; certainly the espresso machines never did them any favours, and I tried every chance I got.
Edit: formatting
[0] https://en.wikipedia.org/wiki/Rubicon_Trail
[1] https://en.wikipedia.org/wiki/Single-origin_coffee
[2] https://bluebottlecoffee.com/preparation-guides/pour-over
[3] https://en.wikipedia.org/wiki/Chemex_Coffeemaker
[4] http://www.hario.co.uk/coffee/dripper.html