That's true for actual spammers (i.e. if they buy your address from a list and so on) but not for legitimate companies. Both examples I gave are real companies that I signed up for. I'm pretty sure if I managed to unsubscribe they would honor it.

No I have many examples in my mailbox from major companies.

Can you name and shame them, like I did?

Looking at my spam folder: Air France, freelancer.com, Addison Lee, Pluralsight, etc. I gave up playing whack a mole with unsubsubribe links that never get honored. I now filter emails automatically by domain name and/or keyword (for the companies that got my email before I switched to this alias system).

That had been my experience for quite some time. More recently it seems to actually have some effect.

As I'd just noted in another comment, many senders use a mail service provider, and a single bad actor can have very bad knock-on consequences, even for mail which doesn't transit the MSP (SPF records listing MSP IP space).

For many major brands / companies, unsubscribes work reasonably well. I've seen some success with this, don't offer email addresses generally, and flag the remainder as spam, with blackhole rules in my various filtering tools.

The larger problem with email is I simply don't trust it any more.