hey philalethes,
yes – it is doing it´s core task of info-management quite well! no doubt!
and thanks for the Drafts 5 hint! these hints are something useful coming out of this thread for me; especially as all things here are discussed in terms of means and ends (beyond singular tools). I can see it possibly making a way into my workflow bec of it´s capture+process capacities – but then it doesn´t seem to solve my issue which is as much about retrieval and display of results as about quick capture.
but in general all this is very helpful for me as well to get my head around how to build a workflow around DT where it lacks some kind of specific functionality.
the ‘in-place’ vs ‘round-trip’ idea coming out of this discussion (thx to scottlougheed) was also helpful to me. as you say indexing external folders comes in handy and can be a critica bridging-mechanism, which is true (and is also why I also rely heavily on indexing vs importing for the core of my files/data). with regards to my short-list of Ulysses + Bear it can help in the case of Ulysses, as Ulysses folders can be indexed/shared this way (the drawback/friction being here that DT can´t display the proper titles bec of Ulysses proprietory mechanism; so ‘only’ the content comes in – but then folder-structure of Ulysses is retained at least in principle)
in relation to Bear I have come to the conclusion that in some cases (like Bear) the fall-back option is really going back to ‘manual labor’ and a ‘shuffle’ solution (adding to ‘round-tripping’ + ‘in-place-editing’ 
). I have found no better solution as to export all Bear notes to a folder ‘by hand’, which then in turn is indexed by DT. the good news is that a sweeping replace of the exported Bear-notes will leave intact the internal DT-information/-structures. thus when you worked with the notes in DT (made an alias/replicant or assigned keywords) it will be retained. so, in some cases this kind of ‘shuffle’-workflow might also be a solution of sorts.
– for me an interesting fringe effect: Bear can export its keywords (which are not osx-compatible tags) as part of the note-content! … this way you have to re-apply these as tags, if needed within DT. but as a side benefit the tags are really globally searchable in DT. looking for ideal supplements and hitting all kinds of roadblocks and points of friction I have learned to embrace and love these fringe-benefits… 
– will keep following what this thread throws up; and in case I find some good new contenders for DT-notetaking-supplement I will report of course.
best! oliver