it wanst noticed in TAD until like 2015-2016 so you are not alone there
but on the point of the incan fort its due 2 interaction that makes them a lot more efficient lets say is due to
1- Wasted damage if the fort cant one shot
2 - weirdness of the aoe mechanic
to demonstrate here is a vid of a fort and a stronghold attacking 15 vet skirm ( the fact that they are vet is important
it can be seen that both the fort and the stronghold kills 15 skirms in about the same time, despite the stronghold doing less than half the damage of the fort
this is partly due to the fact that the the fort is having to shoot twice in some cases since it cant one shot the skirms, this is the more likely scenario since most units will have about 150 hp with range resist by the time these buildings are around
but its also due to a weird quirk of the splash mechanic which comes into play alot more with more units in that the splash damage is spread to the area, so if you have massive splash in an area, you can ironically get less damage to the other units in the area since not all of them will get hit by the splash
where as if you have little bits of splash damage like the stronghold, you are less likely to waste splash damage since its more evenly spread.
against single targets, the fort will perform better like with falcs, but against a bunch of bunched up masses of infantry, the stronghold will perform much better then their numbers say.
increasing their splash area only improves them in this regard, and you can garrison them for more damage.
in most games people have to respect a fort, but they fear the stronghold
)