CD-R are maybe 10 years. Floppies are more reliable. I have plenty of C64 and Apple II floppies that work fine.
MAM-A/Mitsui has tested their Gold reflective layer CD-Rs with their Mitsui dye, to withstand
the full spectrum of light, same as the sun, for 100 continuous hours without damage.
Using data from tests like these, industry standard guidelines predict that MAM Gold CD-R
will last greater than 100 years! (In fact, if you extend the data, MAM-A predicts a lifetime of
up to 300 years before failing at the Orange Book limit of 220 CPS)5,25" floppies (especially lower density variants like the ones you mention) are quite reliable indeed, but the most recently common 1.44 MB 3,5" floppy is terrible.
However, after most people had moved on, when I did use more recently-manufactured ones, they were indeed terrible.
My theory is that, when Zip disks and CD-Rs took over and people stopped using 1.44MB floppies, the manufacturing of them changed, and both the disks and the drives became much crappier than they used to be. The drive manufacturing moved from Japan to Thailand, for instance, for some of the drives I looked at, and the components were noticeably crappier (drive motors much smaller, for instance). These were the days when every PC had a 1.44MB drive just for Windows XP drivers, and no one ever used the drive for anything else because it was just too small, so the OEMs really cut back on the quality since the drives weren't expected to be used much.
But back in the early 90s, it wasn't like that; those disks were totally bulletproof, just like all the other floppies.
Even the Windows support of CDs has gone to shit. Windows 10 usually can't figure out if the burned CD was already ejected and inserted with a fresh one, and randomly retains files from the previous burn.
Ripping audio CDs is slower than it used to be as the drives seem to become unbalanced.
You are right that at some point they started making (much) worse quality 1.44MB floppies (and drives, probably, though I have had nothing but good experiences with mid-2000's floppy drives so far), but I still say they're much less reliable overall than most 5,25" formats.
I say this partly because I have a retro-computing hobby and when acquiring random floppies from various places my experience is that 360K floppies from the mid-80's almost invariably still work fine while DD and HD 3,5" floppies from the late 80's to mid 90's are about 50-75% unreadable garbage at this point. They just don't survive. I also remember having to throw out a lot of 3,5" floppies (name-brand, too; Sony, Verbatim, etc...) due to them becoming unreadable in just a few years in the late 90's.
I mean, it's not surprising. Each bit is simply much physically larger on a 5,25" floppy.
So be thankful they didn't reinvent those, only using plastic instead of paper based card. Though plastic punched cards would last a very long time and also be imune to EMP, water...many things that other forms of media fall foul of.
Just don't get the storage capaicty there and if they are using systems that fit data on a floppy. Well, a CD based media would perhaps be overkill.
As for CD quality, that can vary a lot with some lasting since day one, others - rusting away (literally I have old CD's from the early days, some fine, others have rust holes due to impurities in manufacture).
But like most things, you don't appreciate the quality of the product until time has past and it still just works.
Floppies are really just tape in a disc format, and use heads to read high and low signals and deduce the 1s and 0s.
It stands to reason they should last quite a long time considering audio/video/data tapes can last over 50 years.
I wonder what the capacity of VHS tape is, given the restrictions of the NTSC modulation? I believe, back in the 80’s, someone made a ISA card for PC backup to VHS.
NTSC video signals offer a lot of bandwidth but very very few promises about the quality of the reproduction of the stored waveform