No matter how one coats it, HOI 4 like other Paradox grand-strategy games, but especially HOI 4, is at its core a spreadsheet where the only long-term strategic goal is to make the numbers go up, higher than your opponents in order to crush them. It's a game of optimization basically, to try to make the numbers go the highest as fast as possible. There are many layers of details, systems and controls interconnected by complex formulas - but ultimately it's still a spreadsheet where A wins over B if A is greater than B in terms of numbers, quantitatively and/or qualitatively speaking. Which is why there are so many HOI 4 discussions about the optimal research path, the optimal doctrine, the optimal national focus path, the optimal division template, the optimal factory build, the optimal fleet composition, the optimal ship design and so on and so forth...
So even if the research tree were extended in time, or made more granular, there would still be an optimal subset of technologies to research. Unless the tree were perfectly balanced so that alternative research paths were equally potent, which would be ideal in a pure asymetrical strategy game - but very very hard to achieve given the already high number of technologies, and the need to be somewhat realistic and historical.
Making the technology choices more granular and divergent would be more interesting for the human players indeed, but harder for the AI players. The more choices the AI has to make, the more incapable it becomes. It's already not very competent in its current state, I'm affraid it would get worse. I don't have MtG, but aren't players regularly complaining that with MtG the AI doesn't upgrade its ship designs, and continues to build the designs it starts with, without reffitting the existing ships, or something like that?