Totally agee here. And I'd rather have a chapter every two days with a bit more QC on the dialogues.
I think it'd help quite a bit putting the script through tomething like LanguageTool (it's free: https://languagetool.org/ ) so it can suggest corrections and help catch small mistakes; it tends...
You can experiment with content-aware fill to see if it can clean the see-through bubbles. Also consider that text is going to go in there, so you may be able to get away with doing a less-than-perfect clean on some of them.
I don't get why fan translations are detrimental to the original artist. Distributing raws I'd understand, but fan translations only grow the audience and in practice fan translated webtoons are still picked up for official translations.
(morally the artist still has the right to prohibit them...
If the two groups are willing to work together, why not do joint releases for the new chapters while (also jointly) fixing the old ones? (and replace theold ones as you fix them)
I think that would yield the best results for everyone