I know this has been gone over a million times, but they put it in there to show that orcs were segregated against. I mean that is how economies (including kingdoms and fiefdoms) work; segregate one portion by religion, race, caste, family name, beauty, mental proficiencies, etc. while the other portions reap the benefits. Not passing judgement. Just saying that was the authors' intentions, to show the majority of orcs grew up impoverished.
A lot of good points, but this list is interesting to me for a few reasons.
First, I feel a question needs to be asked. Which kingdoms and fiefdoms are we showing here? If we are segregating by Race, Religion and Beauty then that would change depending on the race or kingdom we are working with, correct? Dwarves are likely found to be less beautiful by Elves and vice-versa. So, the write-up, if it wants to show the status within a kingdom, should give us a kingdom.
Now, looking over everything, it can be assumed that we are talking about a human kingdom. As, well, they are the only kingdoms really mentioned beyond elves and dwarves, and both Tieflings and Half-Orcs tend to be part-human. What does that tell us about your list? Well, Religion is not a concern. The Half-Orc raised in a human society is worshipping the human gods, not Gruumsh. Caste and Family Name? Well, Half-Orcs can be born into any caste or with any family name. A noble family could potentially give birth to a half-orc child. Mental Proficiencies? Well, Half-Orcs have no mental penalties, so we can assume they have nothing special going on there.
What does that leave us with?
Beauty and Race.
So, they are segregated either by their race, or by the fact people think they are ugly... which is because of their race. So, they are poor not because of any other factor, than being discriminated against because of their race.
Which... is exactly the problem I laid out. A race of people being labeled as most likely to be poor, because their race gives them fewer opportunities for advancement.
If it changes, fine. No big deal. But growing up in poverty, just like this quote about gnomes: "gnomes who settle in human lands are commonly gemcutters, engineers, sages and tinkers. Some human families retain gnome tutors, ensuring that their pupils enjoy a mix of serious learning and delighted enjoyment." This quote implies all gnomes are happy. It also implies that they are working class (working for humans) or above in their position in society. (Their economic status is detailed.)
Your quote is wrong on one respect. That quote is talking about "gnomes who settle in human lands". Now, I agree that most Gnomes seem to be presented with industrious traits and intelligence, but they do not lay out the details of gnomes in gnomish lands. Where, one can assume they have candlemakers, soldiers, bakers, nobles, ect.
You will likely point out that the slums detail is also about half-orcs in human lands, not half-orc lands. Which is true. Because there are no half-orc lands. And, we know in Orc lands the Half-orc is either smart and strong enough to get towards a leadership position by killing and fighting, or they are weak enough that they are brutalized by the orcs. They do not have the option presented to be born into a middle-class family, or have a peaceful life. While Gnomes are given that potential in their own lands, and working as middle-class merchants or educators in human lands.
The section on halflings states that most are rural folk in small communities. It goes on to list outliers, but the word most is used as rural. Last I checked, in almost any fantasy world, the country bumpkin doesn't have much wealth. They may have happiness. But not coin. So it is assumed that a halfling's home is modest at best, and their wealth minimal.
You seem to mistake the lore and details. Halflings are pastoral farming folk, but they also are not "country bumpkins". They have large farms and orchards, making them actually quite wealthy. In fact, it specifically says that "even the wealthiest of halflings keep their treasures locked in the cellar" and the image on the page shows a halfling with a lute, as well as some very nice looking ceramics.
They are decidedly comfortable, which is not a state of poverty, and they choose modest and comfortable, instead of it being a result of situations forced upon them.
So when you say "orcs are no more likely to be in the slums..." yes, the authors' say yes, they are. If it gets changed, great. I have no problem with that. Write lore to show their uprising through the classes to where they rule over all of humanity with wisdom. I am fine with that. But that authors' intent was to show the socio-economic workings of the world. And someone has to be at the bottom unless you are on the Enterprise. Orcs happened to be chosen because they had been the pick-on-you race for thirty years. If you want to have a different section in there, say all humans, fine. Dragon Age did it with elves. I believe people liked it. The Witcher did it with elves and dwarves, people enjoyed the setting. So again, nothing wrong with the change, but don't make the authors' intent out to be more than what it was - to try and paint of picture of a fantasy world: its people, cultures, economies, magic, and problems.
Sure, someone has to be at the bottom of the barrel in each location. But see, that is different from Half-Orcs and Tielfings being in the bottom in
every location.
Across the multiverse, according to the PHB, these two races are far and above the most likely to be in poverty. And, if one race is globally more likely to be in poverty because of discrimination... that seems to be a red flag.