dao, nwn2, dai, poe, bg2, ds, and I'm sure many more RPGs (will) have a stronghold/home base system. not all of these get besieged; that's why OP is asking.
why are you trying to dispute that this is a thing?
Why are you promoting the forced imposition of a non-RPG mechanic into our RPGs, like I said in my first post, if you want to play a tower defence game, go play a fucking tower defence game.
Most RPGs have a home base system, it's where you dump all your loot. In Divine Divinity you get to buy a house, in Icewind Dale you get to own the upper-floor of a hotel. What the fuck has
managing a stronghold (read, omg you own a castle that gets besieged) got to do with the price of fish?
You might view it as a logical extension of the concept of a "home base", but it's not once you start "managing for a siege", it becomes a Tower Defence game. Yes, in RPGs your home base area might come under attack, from some easy to kill trash mobs for story-sake (which is what NWN2 turned out to be anyway), but one you start *managing* your base for an *expected* siege, you're just on the path to sidetrack