>If you define "95% of problems" to be "reading and writing data such that data is read and written"
Pretty much. You have a competing definition? With the added point that "95% of problems" are mostly I/O bound reads of unfragmented write-once files and won't see benefit from extent allocation. And of the remaining 5% most of them are database systems which are doing their own journaling and block allocation.
Does btrfs have nice features (I like snapshots myself)? Sure. Do I use it in preference to ext4? Yes. But be honest with yourself: it's only incrementally better than ext2 for pretty much everything you use a computer for. And yet it sits at the pinnacle of 40 years of concerted effort.
And garbage collection is much the same: a staggeringly huge amount of effort for comparatively little (but not zero, thus "worth it" by some metric) payout.
Edit: just to throw some gas on the^H^H^H^H point out the narrowness of vision that I think is endemic in this kind of thought:
> If you look at most drives on the market, you will see devices capable of corrupting data for certain after three years.
If you look at most actual filesystems on the market, you'll find they're embedded in devices which will be thrown out in two years when their contract expires. They'll also be lost or stolen with vastly higher frequency than that at which they will experience NAND failure. If you look at most high-value storage deployments in the real world, they have redundancy and backup regimes in place which make that filesystem feature merely a downtime/latency improvement.
Basically, if someone waved a magic wand and erased all fancy filesystems and GC implementations from the world... how much would really change? Apple has deployed a pretty good mobile OS without GC, after all. Oracle made a business out of shipping reliable databases over raw block devices 20 years ago. Try that same trick with other "difficult" software technologies (video compression, say) and things look much more grim.