It's a cool find, but I'm not exactly sure a wacky optimization exploit means that part of the game is "Useless". That feels a bit like arguing an entire game is "Pointless" because speed runners found a way to glitch to the end credits in 2 minutes.
You can still just play the game without doing that. You don't need wiggle Mario back and forth until the laws of space/time bend and phase him through a wall the end of the level. You can obviously but that doesn't invalidate crushing turtles or stomping turties.
Empire size can be avoided by just buying lots of governors. You don't get level 5+ leaders, but no destiny traits can compete with "all your research is 5x-10x as fast, you need near zero miners no matter how many alloys you produce because every metallurgist has -90% upkeep, you don't even need strategics because habitats no longer have sprawl drawbacks, etc."
The exploit described here is having your cake and (mostly) eating it too: ascend everything to 10 to get -60-80% empire size and the enormous empire wide benefits, but still benefit from destiny traits and leader bonuses. The ability to remove empire size from the game doesn't require this exploit, though. If you're considering spending unity on ascensions (in the current build), you should instead be spending it on hiring governors, then fully ascend your empire for free.
Empire size, as a game mechanic that meaningfully reduces the effectiveness of expansion, no longer exists. Without exploits, just by playing the game in a very obvious way, you can remove it. Unless you consider "I hire every governor I see because hiring each one is more profitable than not" to be an exploit.
This is more like a passageway that leads directly from the start of the game to the final fight with Bowser, that you can just walk along (though it has a DO NOT ENTER sign, aka, the leader cap), rather than map clipping exploits. Clearly, the rest of the game exists, so you're not
supposed to take this path. But that doesn't make just walking to Bowser an exploit.
You don't even need to go over leader cap if you're using Gray Eminence (though you need a great deal of either luck or patience).
The leader cap uses the same mechanics as fleet capacity, plus an XP penalty. Would you consider the (extremely normal) practice of going 2-3x over fleet capacity an exploit on par with speedrunner wall-clipping?