The developers were trying to achieve this, there's nothing new here.

Not everywhere. Moreover, if you don't explicitly set this as a goal, you can worsen, rather than improve, the result, especially when making significant changes to stats.

(I understand that the rest of the post mainly refers to the adjacent topic)

Some players only see one option due to the subjectivity of their thinking, which prevents them from perceiving other people's ideas, and therefore only one narrow solution to the problem. Then they go through their own trials and see the truly correct other solution - again, only one. But there are many such options.

Come on, I can offer dozens of different options, but when you see many solutions at once, it's necessary to understand why some of them are better suited to the goal than others. Why it's better to go directly to the goal, rather than zigzagging.

But here's the catch again: when achieving a good creative-balance, the logic of the original components, which the developers laid down, may change, as well as many units and their models (according to the logic).

Therefore, it's more important to understand what we want: to equalize the upgrades, which is unlikely to take long, or to engage in a long game between forum users and our own minds. The author is the God of creation. He decides how it will be, and we only criticize and evaluate, which, of course, can also influence the result, and may even be better, but each artist has their own vision.

For anyone familiar with my mod, it should be clear that I am not a defender of the original balance and, in many aspects, I criticize it. But if you have set a very specific task - to equalize the upgrades, then you should focus on this, and not come up with something random. And if you really want creativity, it's important to understand what exactly you are aiming for (and not just equalization), as well as that it's foolish to approach this "without fanaticism." Anyone with 2 things can take a good photograph (rebalance): a high-quality camera (experience, common sense) and a beautiful landscape (a successful game), but unfortunately, you can't just slap together a good independent painting (global creativity) on the fly; you need to seriously invest in the process and training, have a lot of time, and enjoy the process. In short, there are no good artists without fanaticism.

I also believe that this approach is the most interesting.
What do you think: do elven archers get "Invisibility" on their own territory?

This is technically very difficult (using a different executable, replacing units each time, scripts), and it's not a given that such efforts will be rewarded.