Darktable is for selecting a series of shots, going through them, developing the ones you want to keep.

So perhaps closer to Photo Mechanic?

It's nowhere near as polished as Photos, but it's capable, open source, and multi-platform. I hope to maintain my photo library for decades, so avoiding proprietary software / service lock-in was my most important consideration. This decision was reinforced earlier this year when we had to do some surgery on my spouse's meticulously curated Photos library: it's damned near impossible to completely preserve metadata when moving items between Photos libraries, and it is impossible to remove RAW files from stacked RAW+JPEG pairs in the Photos library. If I ever ran into those issues in digiKam (which I haven't), I'm confident that my SQL abilities would be sufficient to work around them.

Overall photo editing with open source software is kind of a drag. The features are more or less there, the UX isn't.

One thing that kept me from post-processing a lot of my pictures was the necessity of doing it on the desktop. I'd come back from holidays and didn't really make the time, I guess it can be attributed to laziness.

Nowadays however, I have a subscription for Lightroom and can import the photos on my iPad and edit them on the go, or from the comfort of my couch. I love it.

When I fire up Lightroom classic on the desktop, it downloads everything (originals) I've uploaded on the iPad from the Lightroom cloud. Although this has some inconveniences - it's just dumped into a folder without any regard for organisation - it prevents a complete vendor lock-in. Without that feature I wouldn't have considered this approach.

I love to take pictures, but post-processing is not exactly my favourite activity. I feel that all the tricks I used to get me to develop more on the desktop (e.g. getting a midi board for editing) didn't really get me anywhere, but the Adobe cloud + iPad just did the trick for me.

I wonder why the state of open source alternatives is so sad and what can be done to improve the situation.

I never used lightroom, so I don't know what I might be missing.

(Disclaimer: I may be biased).

Search for "External Raw Import Tools as Plugins". I suggest you take a look at rawtherapee as well. I personally use both darktable and rawtherapee and find rawtherapee to be better suited for some usecases.