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
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
You sound like an expert, but I was very surprised to read this. I bought a Nespresso on Amazon and ended up returning it because the liquid it put out tasted, to me anyway, to be anything but espresso. I tried all the capsules in the sampler pack and disliked all of them quite strongly. I think the biggest turn-off was the fake crema which the machine whipped into existence somehow, but wasn't actually anything like real crema, and ruined the shot in my opinion. There was a front-page post yesterday about the science behind crema, possibly what prompted this post.
I encountered my favorite machine in a house I rented for a couple years which had a built-in/plumbed-in Miele CVA6401, and it consistently produced the best single-touch espresso I've had, with no maintenance except descaling. It didn't compare to a very good coffee shop, but for at home espresso, I'm saving up to get one in my kitchen.
The biggest problem with those things (if you even like their coffee/crema) is that capsule costs add up quickly. 2 people x 2 shots per day... by the end of the year you might as well have bought a real machine and that only gets more compelling the longer you use it. 2 years of that and you might as well have bought a top-of-line-prosumer-does-everything-even-grind-and-steam machine.
The other issue is the beans. Once roasted, beans really need to be ground and used within 4-6 weeks max (even if they're in a sealed bag). The capsules are sealed (probably in nitrogen), but I don't trust that capsules will ever be at the same starting point as freshly roasted beans ground immediately before extraction.
Capsules are a good solution for offices where a real espresso machine would be nightmare of maintenance.
Accept that different coffees are different.
Related HN Submission with comments: https://news.ycombinator.com/item?id=12489523
$600USD and about 2 months later I don't regret a single cent.
Making espresso at home, however, continues to be elusive if you have high standards. The nespresso capsule machines do an OK job but the consumable cost is high and you can't do much to customize it. "prosumer" espresso machines can be hit-or-miss (mostly miss). You really have to tweak stuff to get it right and this includes spending more money than you would think on the proper grinder. Some folks resort to hacking their modest Gaggia's into something greater than the sum of its parts by using PID temperature control (http://www.home-barista.com/espresso-machines/almost-done-ha...). I have a Gaggia and hope to mod it someday when the wife is on a long work trip.
A while back there was an INFAMOUS kickstarter campaign for an attractive, easily hackable PID controlled espresso machine (the ZPM, I think, https://www.kickstarter.com/projects/zpmespresso/pid-control...). It never delivered and pissed a lot of people off (see NYT article, http://www.nytimes.com/2015/05/03/magazine/zpm-espresso-and-...).
I think there's room in the market for a home espresso machine that outperforms current prosumer models... but it is a difficult project!