You realize the more you make this list, the more ridiculous it ends up sounding right?
Yeah, we get it. They are all mortal bipeds that eat. You've described everything from Trolls to pixies. But if you want to argue that there is the same level of difference between trolls and halflings as there is between humans and halflings, maybe move away from things like "can think" and give us things that actually end up mattering to most people.
I mean, if I went up to someone and said "Well, there really isn't any significant difference between a horse, a rhino and a goat" they'd act like I was insane.
And I wonder why this is so important a hill for you to build, but when asked to move past "do they have two arms, two legs, two eyes and a mouth" into something like "how are their cities different" you immediately dismiss it as "conjecture" and put no effort into it. Sure, halflings would build on a half scale compared to humans. Got anything else? Because "human city but smaller" drives straight into what we keep seeing with halflings. Human but small.
And, there are a lot of dwarven, human, and elven cities in the lore. Don't think those are exactly "conjecture" I think they kind of exist, are mapped, and have some noticeable differences.
I literally have no idea how the concept that the various "humanoid" races could be considered "basically human" is so difficult for you? The name is on the goddamn tin.
Separately, you realize your comparison of rhino, horse and goat is like a perfect analog to the halfling conversation we're currently having right?
You say it would be insane to state that there are no significant differences between the three of those creatures but your argument for halflings being basically human is perfectly rational.
The part I dismissed as conjecture includes dragonborn facial anatomy, and racial patterns of conversation. It's the same type of conjecture that leads people to conclude that centaurs cannot climb. It's just the lens you use to view creatures. It's neither factual, nor universal.
The city building would also be my conjecture, but... they take up less space, weigh less, and their stuff weighs less so yes, smaller structures, but also lighter weight materials, longer spans, etc. It also means that halfling dwellings can exist in more locations both underground and above it, for example as tree houses, on cliff faces, etc. In addition, they have a wider variety of creatures that can serve as mounts, with all the agility, speed, and carrying capacity benefits mounts can provide, with far fewer of the burdens so structures and spaces can afford to be generally more accommodating to creatures used as mounts. Do you see how all this starts adding together? Ultimately, I think you are vastly underselling how important scale is to how we live. I mean, would you say that giants are just big humans?
Then,
If you start layering in considerations for how an innately sociable race, that values having a good time, is lucky, nimble, and less susceptible to fear might choose to live...yeah...verrry different.
Buuut.. all of that..is also conjecture, so I'm not going to claim it as absolute truth.