Just an observation that "RW" discs aren't in any way shape or form, stable. My experience is that they fail frequently, after being overwritten perhaps only a couple of times.
Also that DVD-Video files written to DVD-R discs didn't always read correctly. But that may have been the responsibility of the trash DVD burner (Toshiba), which came with my eMachines.
Oddly, I had a freestanding DVD burner by Pioneer, which pumped out hundreds if not thousands of Video discs onto DVD-R blanks, without a hiccup.
The most currently (and formerly), durable media, is good old fashioned silver B & W photo prints, dark stored.
I full well realize it's not germane to this issue either, but I have some 40 year old Ektachrome slides which have been dark stored and are as good as new. Although, I also have some which have faded, or gotten moldy.
You're right thinking that optical media is likely the path to greatest longevity. However, "these kids today", and their streaming habit, along with the extravagant prices of prerecorded DVD & Blu-Ray, are causing the media to fade into oblivion. We just had a news article about Samsung would no longer be introducing new Blu-Ray players.
New computer cases are coming in plenty, without optical media slots, and well, "the rubber band breaks" on most computer burners in a couple of short years.(You push the "eject button" on the drive, and it just sits there and "burns rubber", in a manner of speaking.
So, as a matter of practicality, "the duck did come down", on the "there is no correct answer', answer.
Well Google probably will be around throughout everyone's lifetime in this thread. "Back Blaze" though, not really sure.
Privacy really isn't an issue for not using the cloud. I figure a hacker could make as many copies of your son's 2nd birthday party, and cause no harm nor earn a penny by illegally distributing them.
For the real hardcore stuff like birth certificates, deeds to your property (s), grandma's wedding ring, an old school safety deposit box is the best solution for those type things.