I tried every top email marketing tool

This is very relevant to my industry (escape rooms). Our mailing lists quickly reach 10,000+ and unsubscribes happen often.

I was so focused on deliverability with Mailchimp that I didn’t realize (until I just checked) that I’ve been paying for 2,000 unsubscribers. I had assumed I wasn’t. Deleting them would have moved me down a tier. Strongly considering MailerLite now.

> Deleting them would have moved me down a tier.

Presumably it would also have lost your record of the fact that they'd already asked to not get your email. So you'd have added them back to the spam list if they ever dealt with you again, so they'd have to unsubscribe again.

Spam has gotten so normalized that not only are people not even pretending to get opt-ins, but they don't see why they should have to pay any real attention to opt-outs.

Yes, you are a spammer, and so are most of the businesses on the Internet at this point.

You can archive users when they unsub to avoid them counting towards your billable total

Do you have to manually do this or can it be automated?

Manual afaict.