I'm not trying to be an ass, just asking... what's the point?
You're exploiting a newly introduced mechanic while the game is still in EA with missing and half-finished features. Executions atm only means others will hate you but since diplomacy is missing and incomplete that really means nothing, there's no substantial backlash.
ps1: I love the lore, immersion, the visuals, roleplaying, etc. and the kind of gameplay you described here is most certainly not something I would do...
ps2: I meant no insult
to me you are TTing over a playstyle that punishes you by itself, ruling an empire of ashes and graves isn't much fun, just like managing to conquer the entire map without any sort of Civil War mechanic, some weird Gavelkind heritage, etc. Though if such things would be implemented I imagine the game would have no end (which is good for some, bad for others, people are quite divided onto this subject itself). I'd prefer something more akin to CK2, so, if you wipe out a clan, another rises from within the lands (meaning you'll forcibly get vassals through such a mechanic if you own too much land, and said land should be granted onto the noble, but I think the player should still have some agency over such a mechanic, like chosing a preferred area to appoint new nobles, or choosing which fiefs to grant them)
That being said, internal politics should become a major part of the game to avoid map-painting dead-ends. Both this tactic the OP used, or the "honorable" one lead to the same conclusion: You become the sole ruler and has absolutely zero things to do after that. That on itself is a major issue IMO, but at least in BL it's less absurd than it used to be in WB (in WB the last faction was a nightmare to wipe out, only done the World Conquest twice, and the combination of Wack-a-Mole + pointlessness of ruling everything made it a standard for me to reach kingdom level and leave it at that by using mods that had Diplomacy on them, that way keeping each save a different RPing opportunity and denying completely the idea of creating "The Empire" in any playthrough.)
Some mods would address this differently, either by sheer amount of lands, by a combination of the former with "inefficiency" to discourage world conquest, or by adding post mono-color map "challenges". If BL doesn't adopt any of those it'll be quite a boring ride doing a second playthrough after managing map-painting once. Again, at least it is less ridiculous than WB OP "last faction" thingy, but I've already read some feedback stating they were unable to finish off the last faction due to a stream of forced peaces (impeding the player from conquering any of said remaining faction's territory, peace would be shoved down the guy's throat before he could finish a siege camp).
So, all in all we have to wait, stop going nutcase over this, just wait to see what they want to do with this feature, atm it IS pointless, a gimmick, but a gimmick that can be exploited due to the lack of complementary features. Also, you've said "I'm not trying to be an ass" but your statements sound like you did.
So many people going out of their way to passive-aggressively suggest that this is "playing the game wrong". Hilarious!
To me that's pure idiocy from them, if I wanna cheat a flying unicorn dual-wielding flails in a ****ing SP game, why tf would anyone care? It's basically the cumulus of the self-entitlement, to believe they have a say on other peoples' choices, which I interpret as idiocy, stupidity.... People like that should be in cages because they are actually quite dangerous to others IRL, that's basically the principle of fanaticism, fundamentalism, and the driving engine of any dictator or tyrant... The absurd idea that they have the right to decide how others should do or experience things. I absolutely abhor people like that.