Is the bitcoin blockchain really non-corruptible? Some people say that proof of work is better than proof of stake, because it's not possible to rewrite the whole blockchain on-spot. One would need to "re-mine" everything.

But I think this is not true! A hypothetical attacker can rewrite the whole bitcoin blockchain and make the timestamps make the block-time exactly 10 minutes, and this way the difficulty of mining will remain at minimum, and no real mining is required. The mining effort is minimal.

The way I understand it, is that such a problem is practically solved by check-pointing the blockchain in the source code. The devs hard-code block-hashes in the source code so that no one could do that. Is my description of the situation correct?

In other words: Without check-pointing, the bitcoin blockchain is inherently corruptible and can be destroyed. What am I missing here?

PS: This is not about PoW vs PoS. This is basically about the claim that PoW is non-corruptible. If my conclusions are true, we can just do the same with PoS blockchains and use check-pointing to prevent corruptibility.
Your attack wouldn't work because nodes take the most-work chain as leading, the number of blocks is irrelevant. Any attacking chain needs to spend at least as much work as was done for the original. This actually used to be a bug in the whitepaper and the initial bitcoin software implementation: it checked for the longest chain instead of most-work. It was fixed very early on.

Checkpoints are centralizing as they give devs power. They're no longer done in Bitcoin.