Codifying ANY logic is doable, but especially simple logic like that has it's upsides in how many middle men it can help eliminate, and the TONS of human error that comes with it.
In the examples you're giving, you could have codified "here's what happens if the supplier cannot complete the transaction" or "here's what happens if parties cannot agree on the quality of the work" or a zillion other things that already exist.
You did, however, hit on the big one, that when something goes wrong or something is misunderstood or somehow someone needs to talk to a human...well good fucking luck.
The obvious downside of all the decentralization mantra is that of course it means you're liable for your own mistakes, which is just NOT a business model that ever works. That said, the crypto space has gotten massively more centralized (because it turns out market forces still don't give a fuck about your philosophy), and I think the future of the tech lies somewhere else entirely, where end users functionally never interact with it.
The validity of any transaction can only be determined and guaranteed by the state, so honestly just having the state host a central database seems much easier
It could be used for notarising contracts, recording crop yields, declaring bankruptcies, listing property sales - you name it. Pay $1/kb and your data will be stored forever.
Anyone can replicate the changes to their own computer to validate the hashes and prove the government isn’t changing anything.
I think that would capture 90% of the value of a blockchain with almost none of blockchain’s downsides and it would be trivially easy to implement.
This isn't the case for digital only assets though. There are certainly much fewer digital assets people use than physical ones, but they're there. Domain names, forum membership, entry gates, game skins, etc. How many times have you entered a community and thought it would be great to have a tiny bar to contribution, like a small membership fee, enough to weed out spammers and young children?
This is aside from enterprise oriented chains like Ripple that just use chains help facilitate regular business.
You seem to be arguing that blockchain has to magically solve real world physical problems, but paper contracts don't do that either. You still end up in court. Its just a question of how you are substantiating they really signed the contract.
If the problem was about enforcing a signature, you do not need a blockchain, each party to a contract can just store the cryptographic signature themselves or with one or more trusted custodians. That is a fundamental feature of cryptographic signatures not blockchains. And then you need some mapping from legal entities to public keys, but this might as well be a centralized database run by the government (potentially outsourced to a private contractor), after all in many jurisdictions the government already keeps a list of legal entities and metadata about them.
How would you express any of this stuff on a blockchain in a useful way? We could have “blockchain yelp” but it’s hard to protect that against fake reviews. And seeing a mix of reviews isn’t enough to know if you should go into business with someone.