Converting iPhoto9 Libraries to Sequoia Photos

I have a MBA (2017) running High Sierra. It has 24+ photo libraries, using iPhoto9, all stored on an APFS-formatted, external SSD. My setup is fairly simple/basic, since none of my photo workflow involves either the iPhone or iCloud.

I am now setting up a new MBA (M4) running the latest Sequoia. When I launched its Photos (10) app, I got the message that the older format libraries could not be opened -- I would need to do an "import":

I was eventually able to select one of the libraries and do an import. The results were disturbing.

So, before I proceed down the 'import' path I need to confirm that this is the correct workflow and that the results I got are the best I can expect.

What I got (from the one library imported) were some 3,000+ photos, with none of the edits from the source library, not even the basic 'rotate' for the correct orientation (which is the first thing I always did when bringing new images into a photo library). Of course, all the other tweaks are gone -- straightening, cropping, color adjustments -- all gone.

More disturbing is the loss of:

• organization (structures of albums and folders),
• classifications (the 0-star to 5-star schemes that have existed, and been used, over the various earlier versions of iPhoto)
• keyword tags

While I was used to needing to tweak some of this when I migrated between revs. of iPhoto, I was not prepared for the extensive loss of nearly everything with the new Photos app. (Surprisingly the one thing that did appear to still work was the script/app by Old Toad from about a decade ago to move the filename into the Photos title field!!)

Suggestions much appreciated! Otherwise, it looks like I'll be hanging on to my old MBA and running under High Sierra+iPhoto9 until I no longer can.