I agree that the iMac needs to be usable as a monitor. Both Dell and HP all-in-ones that I looked at do this (I did not do an exhaustive search, so it may not be as common as my 'look at two' makes it sound, but it's not UN-common)

However, let's be real clear, iMac is not a mid-range desktop, price-wise. Amazon's all-in-one category's HIGHEST non-apple price in the top-10 is $599. There are three non-apple all-in-ones over $1k in the top-50. [1]

Obviously, once we separate the pieces out, things become even more clear cut. You can buy the beefiest "mini-pc" from amazon and pair it with a 28" or 32", flat or curved 4k monitor for $200-400 and still have money left over.

The iMac is NOT high-end, but it is luxury, and that's an important distinction.

1: https://www.amazon.com/Best-Sellers-Electronics-All-in-One-C...