According to Gregory Maxwell, even Core does not validate all transactions.
[citation needed]
please, can you elaborate on this? do you have a link or something? I'd like to know what escapes validation.
I understand that things that it reads from disk are not validated, and only a few last blocks are verified at startup, but they were validated before they were written, so everything gets validated. Doesn't it?
I understand your request for a citation. Seems implausible, right? I agree that the burden of proof - as far as 'according to GM' is concerned - is on me. A cursory check does not turn up a quote. I will continue to look. However, you point out the issue yourself:
"only a few last blocks are verified at startup, but they were validated before they were written, so everything gets validated. Doesn't it?"
If one is starting up a new node, and only the newest blocks are verified, you are not verifying the older blocks. You are trusting others to have done the verification of the earlier blocks. Ergo, Core does not validate all transactions.
To some this may be an acceptable risk. However, it is most certainly not operating in a trustless mode.
IOW to answer your question - to wit: "Doesn't it?", the answer is: 'no, it doesn't'.