It is not like any other tactic. When you incorporate other tactics like the ones mentioned (worker stealing, early war, mounted warfare, hut, events, galleon chaining etc,) you still need to achieve 99% of the basic goals that were originally needed to achieve your chosen victory
Mounted warfare that achieves domination is a comparable % of the "basic goal of the victory condition". That aside, the basic goal of the culture victory is also literally unchanged; you still need 3 legendary cities. That doesn't change whatsoever and thus "99% of the basic goals" are also intact when using CtE. What changes is the method used to achieve the 3 legendary cities, just like what changed in domination is the units used and not used. You're claiming the tactic is different from other commonly accepted tactics but it's not true.
It is also premature to assert that culture is materially more complex than espionage, although I admit it is premature for me to assert the opposite also. Neither one of these things is rocket science, and fast times come down to execution for both.
If I spent years designing and evolving the culture victory to see it replaced with espionage, I would want that tactic removed from the game.
This is not relevant to the discussion. "People spent more time on this previously" is not a sensible criteria for banning CtE or any other tactic. As a game evolves, strategies can and do become obsolete in terms of being competitive. What gives

the fundamental right to exist a a VC focus over

? Legacy?
If balanced properly, this feature could/should remain in the game. I'm not sure why I was mocked for suggesting that it is overpowered and needs to be tuned.
Mocking aside, likely because this game is chalk full of things that are overpowered and of things that are not viable. The interesting thing about

is that until this topic came up, it was centered squarely in the latter when it came to a competitive finish for any victory condition. If you want to talk about overpowering tactics,

is quite far down the list compared to basic mechanics like war and tech trading. Going down the path you suggest would make XOTM stop being civ IV and start being "what random balance can we throw in the game without any substantiated numbers or objective basis". It would have to become that, because I don't see anybody doing heavy statistical analysis of each mechanic while mitigating noise factors.
If not tuned, it doesn't belong in the game should be banned because it replaces culture victory, not enhances.
It's still a culture victory. What it is really replacing is how to generate

. You are still generating

, and you're even still doing so with

and GPP.
Early-rush marathon strategies for space are effectively already banned from XOTM, because marathon games simply do not exist in the competition.
I used marathon as an example because it most favors war, but any speed is applicable to my example (unless quick nerfs war too hard in space games, which I doubt). HoF partitions its rankings by speed anyway so that the games are reasonably comparable.
It is in my opinion a degenerate strategy that simplifies the game and completely breaks immersion by rendering all the usual culture related game elements obsolete.
Using terms such as "degenerate" are not conducive to fair discussion. Immersion is a matter of opinion and of only questionable use in making a competitive ruling. I don't think it's fair to claim simplification whatsoever. If it were simple, it probably would have cropped up as a winning strategy five years ago, not right now.
As it seems to obsolete "traditional" cultural victories I would see it as an "unwanted" exploit and either ban its use for cultural victories or have a different victory condition.
Again, it's not sensible to use a metric such as "this is different from what we're used to" as a metric to blanket ban tactics. If we always stuck with a traditional approach, we wouldn't even have intelligent use of GPP and would still be locked in a "CE vs SE" debate, if we even made it that far.
It's reasonable to demand some reason that this tactic breaks the game from a competitive standpoint, not from a "I like the

icon more than the

icon" standpoint.
If this tactic can somehow allow impossible, rule-breaking outputs (akin to glitches like infinite oracle techs or infinite war success/diplo point nonsense) or trivialize the importance of planning and micro optimization, you'd have a legit case to ban it as an "exploit". Instead, all I'm seeing ad nauseum are these statements:
1. This tactic is different from my usual expectations and I don't like it.
2. This tactic is stronger than a previous tactic and should be banned based solely upon the fact that it's a superior tactic.
The problem with such arguments is that they are objectively insufficient criteria for which to ban something in a competitive setting. Why? Because they can literally be applied to the vast majority of standard play innovations over the years. When your ban criteria allow the vast majority of tactics in existence to also be banned, the ban criteria is too broad.
Banning this practice is ludicrous. A separate VC has precedent (similar to RLDV vs UN diplo) if the staff is willing to accomodate it. Actually that's the closest comparable example; BTS feature that allows a previous victory condition (in this case diplomatic) to be won so long before the previous standard that it isn't particularly comparable. I wasn't around for the days when Apostolic Palace was being debated, but what we have here is essentially another apostolic palace, albeit a little *less* overpowered than TAP.
And yes, the game actually represents both UN and TAP as "diplomatic" victories. We only distinguish them here on the forum. CtE vs traditional culture is absolutely identical in scope. Banning CtE would be no less absurd at this point than banning all RLDV...so much so that banning CtE without also blocking any RLDV submissions would be logically inconsistent and suggest dishonest intent (IE wanting previous submissions to stand and thus voting down things that beat them).