Any way to correct original EXIF data?

I put my trust in iCloud Photos to host my ~300GB collection. Periodically, I export everything to a USB drive in case of some iCloud catastrophe. Recently I bought a Synology NAS (DS218+) and decided to tinker with its photo features, but ran into a problem with those exported files.

About 10% of my photos and most of the videos get an OS creation date of 11/18/18, which I recognize as the day the files were all downloaded from iCloud to my new Macbook Pro (finally one with enough SSD space for my entire collection). I understand that the create date could be when Photos downloaded the file, but the EXIF also appears to be missing which is causing a real mess with for other photo products, like Synology's PhotoStation & Moments, but also Google Photos and even Aperture (which I still miss...) since these all appear as taken on that 11/18/18 day.

Some of these photos do have questionable EXIF, like screenshots or super-old where EXIF might be screwy. Those don't bother me too much. But many, like ~1,000+, were shot with real cameras, Nikon D70, D90, and recently a D500 or DJI Phantom drone. New files were all imported directly from camera into Photos and had good EXIF data when imported (i.e. when I imported "Fourth of July 2018" photos in July '18, they didn't import to 11/18/18).

Within Photos, the photos have the correct capture date, and I can adjust them if necessary and they move along the timeline. "Exporting Originals" does not keep this, which is unfortunate but understandable if Photos has lost the original EXIF. "Exporting" with the options for downsizing *DOES* put in the create date as adjusted in Photos, but obviously I don't really want to do that since they're lower quality.

So does anyone know how to modify the EXIF create date *on the original file* within Photos? Preferable automatically? I really don't want to manually correct 1,000+ files. I know Aperture had some great batch EXIF modifying tools, but it doesn't help me since the "good" dates are trapped in Photos' database. And I know there are some decent third-party EXIF tools too, but I don't know if they can modify EXIF within Photos photos.

Thanks!