Spam sent to different domains (especially in different TLD) tends to be different so experience can be different.
In my observations badly formatted spam exists, but have big intersection with the spam which is relatively easy to filter out. Nicely formatted HTML spam on other hand is hard to filter because the only difference with legitimate marketing email is lack of any consent from the sender. Sure I can hit an unsubscribe link and my be never will get spam from the same domain again, but spammer will know that this email is active and will include the address in spam send on behalf of other customers.
Well, that is where the line of solicited and unsolicited mails fall, spammers are generally unsolicited (so no previous mail address confirmation), their unsubscribe links won't work and >90% of them are plaintext with the remainder having bad or illformed HTML. 99.8% of marketing mails I get have an unsubscribe link that works because it forgot to uncheck the newsletter when signing up, those are not an issue. And those are usually HTML mails with well formed formatting.
In my observations badly formatted spam exists, but have big intersection with the spam which is relatively easy to filter out. Nicely formatted HTML spam on other hand is hard to filter because the only difference with legitimate marketing email is lack of any consent from the sender. Sure I can hit an unsubscribe link and my be never will get spam from the same domain again, but spammer will know that this email is active and will include the address in spam send on behalf of other customers.