The last two games I completed by total annihilation, I didn't touch that tree once with any of my Commanders. Once you have 4 or more active Commanders, the 2 extra capacity slots aren't as vital as they may seem, especially if you have the initiative promotion (which you should) which allows for all the maneuverability that you may need.
I have also rarely used the 'extra span of control' for my Leaders, but there have also been times in late Exploration and especially in Modern Ages when I really missed it.
My answer was to buy extra Leaders with the copious Gold income available in Modern Age, but having a 'built-in' extra span of control in the later Ages makes more sense: historically, the size of the armies and the area they covered increased massively, especially in the Modern Age when motorization and radio/telephone communications increased the Commander's potential range of effect from a mile or three to hundreds of miles.
I am not claiming that Commanders don't make a difference on the battlefield but I do know that I have fought off commander armies with just numbers and then killed the commander as range is so powerful in this game. Melee combat is so predictable and and never feels like any real 'edge' has been attained for me. I feel like combat, especially in the modern age, should have some game changers come into play. Not a slow build up of +2s and +3s but actual military advancements that change warfare in a new way. Not "we invented seige weapons again!" as that is what it has felt like for me.
This is an argument going all the way back to the beginnings of 1UPT and the ranged - infantry/melee - cavalry distinction in units. The game has never gotten the relationship among the units right, or the distinctions that made each of them powerful only in certain situations.
Ranged is overpowered because for most of history in reality an opponent could move through the area you could hit with a ranged weapon in a few seconds even on foot and so your archers/slingers/javelin-throwers got off a few shots and then were fighting for their lives - or running for home if they were smart. Ranged was only a battle-winner if the enemy could not get at the ranged units, either because they were on horseback and rode away, or were behind melee units that protected them, or on top of stone walls that protected them even better.
Cavalry is overpowered in Civ VII because they have been given all the same attributes of infantry - ability to entrench, no malus for being in terrain like jungles, swamps, or rough hills that negate their mobility advantages - and also get higher base combat values than the infantry. And, of course, the maintenance and cost of raising cavalry units is grossly under-represented in the game, so that raising a cavalry army in a jungle-based Civ only carries the 'malus' that you are not likely to have Horse Resources to buff them even further.
Infantry should be the basic jack-of-all-trades for most armies, but instead as a result of the misrepresentation of other unit types, they are there largely to provide targets for the archers or be run over by the chariots/cavalry. That totally warps the in-game combat compared to the reality it purports to represent.
The other side of the problem is that once most combat became ranged, with the advent of effective gunpowder weapons (the very end of the Exploration or beginning of Modern Age) all the old relationships changed.
Ranged became Very Long Ranged - artillery, which by 1900 was able to sit back miles away and flatten any unit it could reach. Even before the development of Indirect Fire, cannon had effective ranges far beyond the distance an opponent could traverse without getting pounded, and its fire could both reinforce any defense and support any attack as needed.
Infantry became dominant on the battlefield. For all the highly-publicized cavalry charges and battles between 1700 and 1900, against steady infantry with their muskets/rifles and later their machineguns/mortars/light artillery, cavalry was simply too big a target for their cost. WWI, with the battlefields swarming with automatic weapons and artillery, brought this home to even the most suicidally optimistic horseman, but the lessons had been there for over 100 years already.
'Cavalry' only got its Antiquarian Importance back when they got armor to go with their mobility. In game terms, that was NOT the 'landships' - all the landships represented in the game had top speeds of less than 10 kph - about as fast as an infantryman could jog, and nowhere near fast enough to take over cavalry's traditional roles of assault, pursuit, scouting or screening, that had to wait until the Medium Tank of the late 1930s with decent armor and carrying a cannon instead of machineguns only.
Point is that, AT LEAST by the start of the Modern Age combat factors and relationships of the various unit types need to change dramatically. This, after all, roughly represents the culmination of what has been called "The Military Revolution" - the rise of gunpowder and all its consequences both on and off the battlefield.
