Got permission from
@Vietthai96 to post here.
I disagree with majority of the OP, I will skip what others have addressed and just say what has not been said
The major issue here is really the difference between destroying a space-time continuum and just destroying all the physical contents of a space/non-infinite timeline. Low 2-C was never about destroying all of space or some time in particular, It is specifically about erasing or creating the entire timeline of a space equal to or larger than the known universe, which has to include the past, the present, and the infinite future.
That is what we refer to as 4-D here in the wiki, an entire timeline that continues infinitely.
Point in case from the tiering system: the universe can be seen as an infinite film strip, where each frame is a snapshot of the whole space at a given moment. Destroying the entire film strip the full line of uncountably infinite “frames” that make up time itself is what qualifies as Low 2-C. In contrast, just tearing apart one frame, or even all frames at the same instant (without affecting their flow across time), is only High 3-A.
I think what the OP should be arguing for is what we qualify as a 4-D construct. The real question is does part of a timeline and not the whole thing count as 4-D? Arguments can be made for both but since that is not the OP's major argument, I will leave that aside.
Anyway as it currently stands, what we define as timeline here on the wiki is long stretches of years. if a supposed timeline lasted a million years or a billion years, it would still be High 3-A unless it is infinite and encompasses all points in time. What make it Low 2-C is that the timeline extends infinitely into the future and the past is also part of that continuum.
For your other point, any universe/timeline is considered infinite unless stated otherwise, so unless it is not said to be infinite or it is said only certain part is destroyed, it is assumed to be low 2-C.
Tldr: It is not so much about what is getting destroyed but rather what we qualify as 4D on this wiki, and spaces lesser than size of the known universe, is not agreed to be 4D here even if the timeline extends infinitely.