It's honestly not that hard. Given that both parties are serious about working together, even considering rescinding a signed offer is ridiculous. There aren't many reasons why a company could legitimately back out of an employment contract, and those can be added to the fine print. If the company want to be protected against potential criminality or an injury that would cause you to be unable to perform the duties of the job you can write that into the contract.
Curious if you've ever done this personally? I've only ever worked at companies with tens to hundreds of thousands of employees, and my perspective has been that the bureaucracy is such that any nonstandard interaction with the company is pretty much off the table.
Same. I asked to make a minor revision to my contract at a 400 person company (related to a noncompete clause that was probably unenforceable anyway - I didn't even ask it be removed, just asked that the industry it applied to be specified). "Legal" said this is our standard contract, we're not just going to change it for you.
A good analogy might be those interactions are off-the-menu but very much on the table, you just need to state your case and be worth it for them to entertain the detour
I'm sorry, but getting a guarantee of 9 months of salary for anything is actually extremely hard when negotiating contracts.
You also seem to be confused about the prevalence of "employment contracts". Aside from a few executives, most employees don't have employment contracts. Your offer letter is not an employment contract.