The correct criticism of iMacs is that it links two parts with different lifespans. There should be a legal requirement that all-in-one computers have an external connector so that if some other component fails or simply becomes obsolete you can use the perfectly functional display with another system.
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...
Most of the cost of an iMac is the display and as your example shows, you don’t see significant savings unless you accept massive compromises on quality. 1080p FHDs is like saying you have a luxury car because your baseline is a golf cart and most of those have terrible color quality according to their spec sheets even if you ignore the low resolution. By the time you’re getting to models which are only one generation behind on CPU you’re looking at a $900 system with a display which is worse than what Apple shipped almost 20 years ago.