essentially, isn't this what mining does?
we do all the hard work, save the results - eventually every single hash will be decrypted & linked to its digest...
sha256 security? getting less by the hash
First of all a couple points.
1) We don't save all the work. We discard about 99.9999999999999999999999999999999999999999% of the work.
2) Even if we saved some work the hashes only provide a lookup for the source (plaintext). Have you looked at what we hash? Not very useful outside bitcoin
3) There are 2^256 potential hashes. The network is ~9TH. Lets pretend it has been 9TH since the begining. Since the start of bitcoin we have hashed (and thrown away but lets just pretend we didn't thrown all those hashes away) 5.67648E+20 hashes.
That is 1 in 1/203,985,725,726,711,000,000,000,000,000,000,000,000,000,000,000,000,000,000 of the potential hashes in SHA-256.
If the hashrate was 1000x higher (9 petahashes) and we hashed for the next milenium and saved all those hashes and constructed a high efficiency lookup table we would have roughly 1 in 1/ 407,971,451,453,423,000,000,000,000,000,000,000,000,000,000,000,000 of the SHA-256 space cataloged.
2^256 is a much (by magnitudes) larger number than you think it is. However large conceptually you think it is take that and square it and you likely still aren't close.