This is quite easy. Brand a might be piece of junk that in a few years will be impossible to find parts for vs brand b that has a reputation for quality and supplying parts for years after ceasing production of a particular model.
You are correct that that is a variable in the comparison. It doesn't negate the comparison. I don't need to compare different brands to get huge difference in cost per hp. I can find examples that are nearly as dramatic within a brand and already cited one (Kioti DS [or the new DK] vs Kioti NX). Besides, neither Mahindra or Kioti are junk!
Not only that, but dollars for dollars doesn't take into accounts ergonomics and ease of operation. For example I would never buy a Kubota with a treadle hydrostatic pedal. I don't like them at all. Others don't like the two pedal system and like the treadle. I sit on my tractor enough that I would gladly pay more for a tractor without a treadle.
Comparing everything that is available for a given price interjects a huge number for variables. But if many of those variables are not important to the buyer what does it matter? For example, I don't care about suspension seats and cup holders. I do care about leg room and my tractor has a nice open platform and lots of leg room especially with my $10 seat modifications. I care about visibility to the bucket and my value tractor has better visibility than most. Another person may have the number of cup holders as their #1 criteria for buying a tractor. What criteria are important is an individual choice. So when comparing HST and gear, tractors without an HST option should not be excluded.
Dollar for dollars also doesn't take into account brand loyalty which is huge for some people. I know that it isn't logical to be that way but as far as I'm concerned that's part of what makes people interesting. If we all thought the same way it would be a very boring world.
As stated above, there are similarly large differences between HST and gear within brands. Mahindra has a huge heavy ~40hp gear only tractor for the price of some of their ~30hp HST tractors. My JD dealer couldn't get me into a 4000 series cut for the price they would give me for a 5055E power reverser. I already mentioned the Kioti NX to DS/newer DK example. The DS was replace with the newer DK which is not available with HST.
By limiting yourself to comparisons between HST & gear within the same make/model, you eliminate a vast number tractors only available with gear transmissions, which makes no sense if you are a person who would consider a gear tractor. There are many people who think value gear tractors are the perfect solution for them - these people make the works interesting too :thumbsup:
None of my reasoning is flawed. I have a different and more value minded perspective than you. If I could have bought an HST tractor with similar capability at a similar price, I would have done it in a second. But HST and similar capability was ~40% more expensive in my case. So many, that price is worth it. To me, and many others, it is not.