Sorry it took so long to get back to you, life intervenes some times.
As to your specific questions and comments:
Photo Mechanic was until recently just a browser, and it is still available as just a browser. Photo Mechanic Plus, which was released in late 2020, adds the cataloging features.
Photo Mechanic Plus allows you to create multiple catalogs, and for my workflow I have two, one for my originals, including raw files, and one for derivatives, which has all of my saved edits. You could have one catalog with both raw and edited files. It is also possible to search across multiple catalogs to return a set of images which would include both the original and processed images, allowing comparison between them. But only saved images can added to catalogs.
I could see a workflow where I create a catalog for each current photo project, containing all my files, originals and processed images, while still adding the files to my two archival catalogs (originals and derivatives as mentioned above) and once I have completed the project I could then delete the project specific catalog. I've only been using Photo Mechanic Plus for about a month now, having upgraded from regular Photo Mechanic.
Note that certain file formats are not supported, such as Affinity .afphoto files, as Affinity does not publish file specs. So if saving files in one of these formats is important, Photo Mechanic is not the tool to use. I don't have this issue, and files can always be saved in a supported format. This is true of both versions of Photo Mechanic.
And I prefer a standalone DAM which just creates a catalog on top of the file system as tools come and go, and I don't want to have to migrate. With the catalog tools I've used I just need to point the tool at my file system and build a new catalog.
As I've not used Lightroom nor Aperture, and quickly gave up on Luminar as the integrated catalog feature brought my system to a crawl given my catalog sizes, I have no real experience with the benefits of an integrated system. As I note below I've been doing this for awhile, and have found a workflow which works for me. I also understand that keeping everything within one application, or application family, would have its appeal and benefits as well.
And some background info as to why my workflow is as it is ...
I started with Photoshop in the late 1990's, before Lightroom, Aperture, and integrated DAM/Image Processors where a thing. And I started using iView Media well before the sales to Microsoft and Phase One. And I've been a Photo Mechanic user for many years as well. I say this not to claim any special status because I've been at it so long, but rather to show that I've built my workflow habits over time. And perhaps more importantly that I'm old and set in my ways!
Second, back in grad school I studied Computer Science, and used Unix quite a bit. One of the philosophies of Unix is a specific tool for a specific job. I bring this up for two reasons as well. One, I'm thus predisposed to using single purpose tools. Two, I do not mind working at the computer. Unlike many photographers I actually enjoy post processing. It also takes me back to my wet darkroom days (I told you I was old!). And so moving between programs is not an issue for me.
Finally, photography is a hobby. If it was instead a job, and I was under time pressure to process images, and processing images took me away from time spent on client photoshoots, then I may be more predisposed to the perhaps more efficient workflow an integrated system would provide.
Anyway, I hope this answers your questions. And like many such applications, Photo Mechanic Plus has a 30 day free trial.
Have fun.