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Not tagging David because it seems he got the point
@Calc Members(yes, ik, this isn't working as a tag, but whatever)
Ok, since this is going nowhere this way, so, as already suggested above, we should each just make a comment summing up all of our relevant points and then we let the Calc members decide what interpretation makes the most sense to them, although I also kindly ask them to also justify their choice so no one has any complaints. If you agree, drop a reaction.
Also, do not reply to other summaries when making yours

Guess I'll start:
I'll say it by now, after re-reading CFYOW, I came to the conclusion the current calc ought to stay

Debunking the points in the OP
First argument: Grimmjow moving zig-zag, "lightning-like", but not at lightning speed.
Well, whether the statement currently used also reffers to his speed or not, which, I must admit, is a bit vague, the truth is
Grimmjow in base form did blitz Ginjo, Tsukishima and the others from so far away they had to use Spiritual Pressure perception to sense him(you can also see how he bulldozed through lightning in the scan) although Ginjo could react to a sneak attack
at a close range with
something close to lightning speed from a blind spot, Tsukishima reacted to a
genuine lightning and
had enough time to insert his sword into a tree and change its past, base Shinji also dodged lightning from a close range and so on.
Moreover,
Tokinada can react to lightning speed attacks at a close range and he struggles keeping up against Ginjo
Thus, scaling his speed to lightning speed should be fine.
Second argument
This one is blatantly wrong, Ichigo wasn't free-falling, he was "hurrying like hell" and we repeatedly see him accelerate.
The other 5 args
They are all basically invalidated by the fact
Soul Society is not a planet. The
parallelism between the Soul Society and WotL of the Living mentioned in the OP
reffers to the dimensions, which we already accept to be universes,
not to Soul Society's ground and Earth.
Soul Society is just a huge flat place, where the day-night cycle is in the same stage for the entire world:
Moreover, it is explicitly a place with different laws(right under the title)
Here I mentioned an example of such different laws, which render any gravity or size related argument regarding the distance(which includes the last 5 args in the OP)
pointless:
What evidence do I have to show when you already have the things OP argues against, or the flat Soul Society having the same gravity on its surface as that on Earth while its flatness also implies it must be smaller than Earth, as you say, yet the gravity being similar to Earth's implies it must be way larger? The truth is that we don't have any way to know Soul Society's size unless we are using Muken so any argument based on things related to it are invalid, whether they are for wanking or for downplaying the true value.
There is no way to determine Soul Society(ground)'s size except using Muken, which the wiki doesn't seem to accept currently. If we were to use
Muken, the ground is just an infinite flat place. Regardless, using Earth cloud height when we don't know the size of the place, several laws, including gravity, work differently than IRL and it's not even a planet, but a flat place of either unknown or infinite size is just wrong.
Answering the 6000 seconds thing
The 6k seconds are just the amount of time it takes for the barriers to close back after Ichigo arrived in Seiretei. However they are talking about this dome above Seiretei:
And other 71 barriers whose location is unknown, so we can't say whether they are near Reiokyu or a few meters above the Seiretei Membrane. The full quote:
The number of Spirit Particle
in Seireitei is falling!
What's going on?
There's a hole... in the Spirit Shield!
So the "key"...opened the port.
The Shihakusho that Ichigo Kurosaki
is using is probably an Ōken fabric with bones and hair of members of Division Zero. Thanks to its durability and protective qualities, Ichigo Kurosaki was able to break through the 72 layer barrier that exists between the Royal Palace and the Seireitei unharmed. However... based on regenerative rate
of the Spirit Shield, It'd take 6000 seconds before closing again.During that interval, a crack opened that allows the passage to and from the Royal Palace.
So yes, there is absolutely 0 evidence that 6k minutes is a reliable timeframe for anything.
Conclusion:
I suggest we leave the current Calc as it is and wait for Cour 4 which will come within less than 2 months when we most definetely will have a cosmology blog and perhaps Kubo will give us more usable details for the Reiokyu-Seiretei distance.