I think you have some weird idea about how fansubbing works, especially when it comes to BDs of a tv show.
There's really zero reason to take someone elses scripts and then TLC/edit them. If you're doing that kind of effort you'd start from scratched, since it'd be way easier. There's zero reason to choose to use someone scripts and then what to change it enough to need a TLC/editor.
And since sushi exists now, it makes the whole 'muxing with shareraws and then things are off' issue pretty hard, except for edge cases. Especially considering the specific situation we're talking about here is DDY vs CGi.
You really think that edit/TLC (especially light amounts, like for a disc release) is more difficult than starting from scratch or you may as well start from scratch if making that kind of effort? Then why does anyone edit CR, Funi, or other official sources for TV releases?
In any case, the reason to change anyone's scripts to that level is if all of the options suck. Some disc releasers do change things even if the original doesn't suck, though usually not at a level to need TLC.
To be honest, backing up a bit, I think most of my points admittedly have to deal with issues that are largely no longer factors. For example, most scripts now don't suck and there's little reason to make much effort to change things.* All this is largely unrelated in the 2015-2016 DDY vs. CGi BD release context anyway, particularly considering they're both using Vivid scripts. Furthermore as you've pointed out, these days you can use sushi.
*though potentially not true if you're attempting to cobble together a release from multiple source scripts. I remember a project along those lines starting for Oregairu but never finishing. I also recall a hypothetical Angel Beats disc release that never turned up.
Anyway, this whole thing started from an offhanded remark at a heuristic that I think at least had some merit in general in the past but is not as relevant anymore and not relevant here, so you're right to point out many of the things you did.