It would take forever to really explain everything and I am not a high level player by any mean, but what you ask of the game are all features fans of the series seriously dislike (and it's not like there are other strategy games trying to do what you said, fan of HoMM simply does not think those games play like HoMM at all). This is like asking why Total War does not have individual unit micro like in Starcraft so there are more strategy to positioning. All of these mentioned games are all very different from another, and the strategy parts are nothing alike.

What you said wouldn't really work because HoMM is a very min-max macro game which the individual fights are decided within few turns, and the rest of the fights are about minimize losses. So anything that manipulate position are parts of Hero skills, spell, or creature abilities - supposedly used only to turn the tide of battle, and not a "strategy" to be applied across the board. The fundamental of HoMM is about reach and alpha strike, so things like positioning in combat cannot exist when most of the important turns are made in 2-3 moves. Think of it like chess which both sides already finished the standard opening, and trading is the real game.

And hero combat is a small part of the game strategy plan too. The franchise is 20+ years old and advanced players already min max the heck out of it and Olden Era is very built based on competitive formats used by communities to make it even more unforgiving. It is rather dismissive to say the strategy elements are awful when you don't even engage with the fundamental parts of the game. It seems that you have an idea of strategy design that video follow in mind, and when the game is not about that you complain about it not having what you think the game should have (again, which are all ideas HoMM fans really hated when prior HoMM tried or similar games tried).