Even if the unsubscribe link works I still report spam as spam. If it is unsolicited then it is spam, plain and simple.
After feeling gaslighted by some spam emails that I was very sure I had unsubscribed from, I started keeping a spreadsheet to track my requests with date, and what link I followed to get removed. Almost 25% of my requests have never been honoured, it's disgusting.
But when you have dozens of databases, each owned by a different company, and they feed off each other perhaps once a day, then you can end up with a long time before all your data is deleted.
Even worse though are places like Atlassian, which add a footer to some of their emails like "this email can't be unsubscribed from".
Even though it's directly illegal for them to have emails that can't be unsubscribed from.
It's their own special "Fuck You!" message to their email recipients.
But the concept of your comment "they're just doing what they want because they reckon they can get away with it" is pretty common among large tech companies.
Those links are often spammer controlled and just confirm your email address as valid.
Personally, my email is text only. It drops all HTML. I prefer it this way. :)
I own my own email domain, and I use a different email address per service. I have done so for 13 years.
On legitimate emails, unsubscribe works correctly almost every time.
True spam seems to originate from a handful of compromised services like LinkedIn, parkmobile, etc. I don’t hit unsubscribe on those, but I don’t see how it would make things any worse.
They get the spam flag too for not being respectful of my inbox.