1. Sorry, but this is very disjointed and none of these pages you've linked to are clear about how to get the title of a parent of a child post.
To get the title of a parent of a Child Post when those are related using Toolset Types you will use the Toolset API (if you need to use PHP; like in this case):
https://toolset.com/documentation/customizing-sites-using-php/post-relationships-api/#toolset_get_related_post
There are code examples in that Document, that shows how to get the data of a parent post.
This can be adapted to your case, and used in the code that calls the data to display in the column.
2. The way that relationships between posts are created is actually very disappointing in Toolset. If I must know custom code to make the relationships useful, that's not good.
I apologise that you do not like the relationships implemented. I suggest to sending suggestions for more features here https://toolset.com/home/contact-us/suggest-a-new-feature-for-toolset/, and if you see usability issues, please let them know us here in the ticket, so I can escalate them
You do not need to know any custom code to use those relationships - you can do that easily in a View, or single posts, using ShortCodes, as our DOC explains (and the GUI as well). More on that here:
https://toolset.com/documentation/post-relationships/how-to-display-related-posts-with-toolset/
However, you need custom code to display those in the posts column which is something simply not supported by Toolset Types.
3. Maybe relationships should follow are more relational database approach where two fields join the tables and they are available to each custom post type
This is what was before, and not powerful enough for the Toolset users, who asked for real Post Relationships and not custom field references, which is still possible to do (with the Posts Reference Field) but it's not a "real" post-relationship. Now, Types stores the relations in Custom Tables which relate to the posts and hence bring performance and usability improvements.
You can however always suggest such changes to https://toolset.com/home/contact-us/suggest-a-new-feature-for-toolset/
We cannot handle such feature requests in the forum directly, unfortunately
4. This lack of functionality seems to be a major product design flaw. I did add it to feature requests, but your product team really should have thought through how relationships between posts need to be used by end users.
Well, I am not sure I follow here.
Mostly those are displayed in the front end, and as I said, displaying them in the backend posts list is only half a "feature", as it would not apply to many to many relations (it simply would/could become too large data to be added to the column).
Relationships can be currently fully set in the backend, front end, and displayed in both single edit backend and front end lists or single posts or else content.
I think this is very powerful but of course can always be improved (mainly in Forms where it is not supported as extensively as the backend, for example).
Our Product Manager will consider the suggestions sent in, and eventually things will be implemented in Toolset if decided so and considered useful by several users and Product Management.
Please let me know if I can further help on the taskk!
