Other users may have some useful suggestions, but honestly I don't have a good answer for you. But let me wax philosophical for just a second.
Many or most genealogy database type sites these days will present you with a completed "citation sentence" - what RM calls a footnote sentence - that can be copied and pasted into your desktop genealogy software or can be copied and pasted into your word processor if you were simply creating a report with a word processor. But if you were to paste such a "citation sentence" into RM, where would you paste it? I don't think there is a good place. It's like you would have to deconstruct the sentence so you could put the data elements into RM's source templates so RM's source templates can reconstruct the sentence. For example, why can't TreeShare simply transmit ancestry.com's "citation sentence" to RM and why can't RM just use it as is without the mediation of Source Templates on the RM side of the house?
RM (and I think a good bit of other desktop genealogy software) is all about source templates and fill in the blank with individual data items and the software will generate the "citation sentences" for you. And RM (and I think a good bit of other desktop genealogy software) is all about the "Source + Citation" model which RM calls "Master Source + Source Detail". What sense does that make if other software will already create your "citation sentences" for you?
I get older and crankier every day. And the older and crankier I get the more I wonder if the "Source + Citation" model even makes sense anymore. And at the same time, I suspect that if you were to get the exact same census page from ancestry.com vs. familysearch.org vs. findmypast.com that the "citation sentence" that you could copy and paste from the various sites would not be even remotely compatible with each other. I would like my footnotes and end-notes to at least have some sort of internal consistency within my own database and within my own reports.
So I use source templates of my own design in RM and I enter all sourcing data manually to achieve a sort of internal consistency for my "citation sentences". I don't use ancestry's pre-constructed sentences or familysearch's pre-constructed sentences. I'm sure you can see the contradictions and internal inconsistencies in my arguments here. I think it's all a mess. I can't think of any good way to make it not be a mess. And there is surely nothing you can do to make me happy about any of it!
I agree with what you are saying about sentence structure, and I have been struggling with how to handle sources and citations for quite some time. I really don't see the benefit in having to enter source citation details into the RM source templates, just so RM can create sentences. All this seems like redundant work to me. I also agree that TreeShare should just simply transfer the "citation sentence" into the source details tab.
I am currently doing the following:
1. Create and name my own "master sources" (using one of RM's templates).
2. Use my "master source" instead of allowing TreeShare to insert a new one in my database.
3. Copy the "citation sentence" from the external source (Ancestry, FamilySearch, etc) and paste it into the "citation details-research notes" section.
4. Copy any remaining "citation details" from the external source, and paste them into the "citation details-comments" section.
5. Do not populate the "citation template" fields, leave them blank for now (in case needed in future), with maybe the exception of the "person of interest" field.
This seems to be working well for me, and I have not noticed any significant report issues. Assuming that I cannot find some tool or method that can "form fill" for me, I will just continue to do the above.
Thanks for the feedback.