If you're not looking at Lightroom for its editing capabilities, and just considering it for its organizing and keywording and facial recognition type of capabilities, I think you would be wasting your money. Especially if you are considering Lightroom Classic CC. It is subscription only, and is $9.99/month in the US. Of course that includes Photoshop CC and you can look at the cloud based version of Lightroom as well. Another thing to consider is that Lightroom doesn't actually make changes to the original or master images. As far as your keywords are concerned, or your "smart tags" or your facial recognition tags are concerned, it would be necessary for you to export copies of those images from Lightroom in order for them to have those tags attached to the files themselves. The master images would remain untouched, unmodified, none of your identifiers attach to the files at all. All of the information would be stored in the Lightroom catalog which is a database.
For years I've been hanging on to picasa as a photo organizer, simply because it worked and I had invested a lot of time with the facial recognition to tag a lot of people. It's (past) time to move on...
I'm now looking to switch to something modern (and supported). I've researched both Adobe Photoshop Elements and Lightroom Classic. Both seem to provide photo management and organization, but tackle it slightly differently. I want something local, I do not want a cloud based service for now.
Lightroom Classic CC is not cloud based. All of your photos must be stored on your computer or attached disk, not in the cloud; and the program itself runs on your computer.
1) How "smart" is the smart tagging feature in Elements? Is it able to learn anything, or are they limited, pre-canned kind of tags like "beach" and "dog"?
I don't know, I have never used it.
2) Both LR Classic and elements seem to do facial recognition. Is one particular better than the other? It appears to me that Elements does the smart tagging for things beyond faces, but that LR Classic just does face recognition. Is that correct?
3) How different is the experience in both for using as a photo organizer? I don't care much about editing, I'm just looking for something that can take 100k+ pictures, and help me organize by date, location, people, places, and potentially "things".
It is my opinion that the Lightroom Library Module is a far superior piece of software than the Elements Organizer. I have used both and I would never go back to the Elements Organizer. Not only (again my opinion) does Lightroom have fewer bugs in the Library module than Elements had in the Organizer, but Lightroom has more features as well. Lightroom gives you more options, and many of the organizing tools are easier to use in Lightroom than in Elements. Either can handle 100K+ photos, and can organize by whatever criteria you want.
4) I'd prefer something that doesn't manipulate the original image. Not sure if either of these applications do that, or how they handle that.
For organizing, neither manipulates the original image. But it sounds like you are talking about editing here (are you?) in which case Lightroom never changes the original image, while Elements does allow you to overwrite the original image if it is not a RAW image. If the original images are RAW, then neither software will allow you to overwrite the original image.
Lastly, in my opinion, organizing is a very human activity and while software can do parts of the organizing task, it can't do all of it, software probably can't even do half of it. You have to put the effort in to achieve organization, no matter what software you use. If you don't then you get lousy organization, or minimal to no organization, regardless of what software you use. So step number 1 would be that you have to commit yourself to doing a thorough job. You can rely on software for some of the work, but that won't really get you too far.