is not technically related to this, especially not in the context you mentioned, since this issue clearly existed before 1.5.the rapid progression of traditions
But I'll agree that the introduction of Unity did not change anything (as many might have hoped, albeit Wiz never said Unity was a mechanic supposed to support tall empires).
Other Paradox games already do that for the military. HoI has stacking penalties and EU4 has morale and combat width. Throwing more men at a prussian army in the mountains will not work. That is what Stellaris needs. A point where getting bigger, be it in fleet, army or empire size, will produce very dimished returns or not work at all.
The big point you're missing here is the fact those games have TERRAIN. (Not in the 'terrain types' of way, to preemptively clear out that missunderstanding).
In Stellaris, there's nothing suchlike. Fleets can pretty much go anywhere from anywhere, except for Hyperlanes.
Thus, there's no 'splitting up troops' or 'defending chokepoints' or 'good defense positions' which would require and therefore promote tactical maneuvring. The best difference between System A and System B in Stellaris might be whether it has a colony in it to siege down for warscore, or not.
Therefore, this is an issue that I am not willing to simply attribute to tall vs wide, but to the inherent flaws with the extremely high mobility of the current FTL methods (excluding Hyperlanes).
And, which is at least some form of positive here, Wiz said he's fully aware of that issue and is intending to completely rework FTL to make these military maneuvring matters actually relevant once he has a patch worth of time to actually go in-depth to rework FTL without relying on bandaid fixes.
Until then, it's relatively pointless to complain about the overpowering strength of wide vs tall, and it might be more reasonable to focus your creative energy on devising a good concept to rework FTL to enable the need for fleet maneuvers and allow a warfare system that is in-debth enough to support 'the few standing against the many'.