Not every magewright produces things outside of reach for the poor. Keith did a pretty good post on them & they come up in wgte plus a little in mormisc/rising. Some of the ones he mentions are chef, launderer, lamplighter, locksmith, medium, & oracle. A poor person can eat at a restaurant where a chef makes food even if it's earlybird special or with a coupon, but they can afford it. A poor person might not have lights that are as fancy or ubiquitous as a middle class or wealthy person, but they might be interested in & able to hire a lamplighter during the off season or maybe they buy a light made by one & try hard not to lose or break it. Similar goes to all the others. A poor person who has a job that requires nice clothes will be getting paid enough to afford the services of a launderer who can ritually mend their nice work clothes for a whole lot less than the cost of some one off first level spell casting even if it's still a first level spell... That launderer's specialized ritual mending is limited to clothes & won't help with your wagon's broken axle.No. The middle class, regardless of how they are made up, must be producing goods and services that all three socio-economic groups can afford.
Capitalist societies are driven primarily by poor and middle class spending, but the middle class can’t do it alone, it has to be middle class AND poor spending.
And most middle class vocations are magewrights or equivalent. Ie, blacksmiths and cobblers are trained in a guild structure that generally includes minor magical training.
I think you might be confusing "poor people" with "penniless refugees who traded away everything they carried with them". According to google "he average price of having a baby, through vaginal delivery, is between $5,000 – $11,000 in most states" That is several weeks or months pay for most people, yet people find a way. The same goes for dry cleaning... There are many expenses that people find a way no matter what
Pretty much all of the economic stuff in the PHB is written for FR & settings with a similar manorial economic system & breaks down badly as you move away from it towards things like eberron's industrial/postwar economy or darksun's post-apocalyptic economy. In eberron you've also got service industries other than taverns & stuff like low skill scratch mages who couldn't enchant their way out of a wet paper bag but go to work on an assembly line placing one piece of an enchantment on a widget before handing it down the line over and over again... those are examples of people who probably aren't middle class, but they are comfortable enough to have the occasional movie at a Phiarlin scryhouse & meal date night out and such.... They might not have a closet full of glamourweave outfits, but they might have one or two they picked up secondhand* & save to wear on special occasions.Yeah, that is wildly at odds with the impression given by descriptions of towns and cities in Eberron.
I really think Eberron is just a world where literally no wordlbuilding numbers match the tone and description of the world, and are thus best ignored.
*or thirdhand or fourthhand