Well you can't reverse sha256 to get the same message back, which means even if you manage to reverse it and find a message that hashes to the same output hash, you have just found a hash collision, because the original message could be anything.
That's for hash functions, which I know nothing about.
For elliptic curve, which still I don't know anything about but can speculate based on experience.
You don't need a quantum computer to break it, you just need a mathematical formula which could work for any number, and since private keys are numbers, finding such formula can solve any key by using even a mobile phone.
So it doesn't matter if your private key is 256 bit or 40 or 2048 bit numbers, because finding such formula is not related to how big a number is, it depends on mathematical relations between numbers.
Almost everyone base their opinion on already existing algorithm and calculate things based on available data, but I haven't seen anyone working on finding or developing new algorithms.
You might think Einstein invented atomic bombs, or the relativity, no they were there even before the big bang, he just discovered them in 20th century.