My library is large too (roughly a third larger). After years of far more complicated storage/backup solutions, I settled w/ a second Photos library on an external hdd w/ optimize storage disabled. I plug the drive in and open this library every so often to update and then duplicate the drive for an off-site copy. Day to day, I use a Photos library on my primary drive with optimize storage enabled.

I’ve found unreasonable value in being able to search through hundreds of thousands of photos from my phone, so I went all-in on Photos.app. Though one enabling factor is that my photography workflow has drastic simplified in recent years to doing very little post (except for astrophotography, which I try and keep wip out of Photos.app anyway).