That's not my understanding of how it would work. If you replace the text in the resolved version with the red text, the chnge will disappear completely from the diff, because the versions will be the same. That is the automatic behaviour when you re-evaluate the diff. If you then make another change to that area in the edit view (or to any unchanged area), then a diff will show in the diff view again
@CalebJohn I think what would mitigate this significantly is adding the ability to sync conflicts, so that if the conflicts are too hard to resolve on mobile, you can resolve them later on a computer. On a small screen indeed it's hard to make any good solution. One of @laurent's earlier comments suggested he didn't want to deviate too far from 'standard' solutions used on other apps, so maybe rather than making a non-standard solution to attempt to make it better on mobile, more time should be focused to make conflicts able to be synced. I posted a couple pf thoughts about that on Please synchronize "Conflicts" folder - #2 by mrjo118
I also think if you try to re-invent the wheel to make diffs more readable, you're at risk of introducing bugs which cause rendering diffs incorrectly or causing a crash. Like I said, the current proposal follows GitHub style unified diff, which is quite standard and there are certainly libraries available which can create the internal representation for rendering this way
The 'use this version' button is a convenience for if you want to take the whole line, but if you wanted to take a section from the line only, you could select and copy the section you want in the diff view (in the red), switch to the edit view and paste it over the relevant part to replace. If you used word level 'word processor track changes' style diff like Keshav suggested, this could make it significantly hard to transfer over a block of text within the line if it is broken up by words