Unfortunately, the google calendar option doesn't actually reject invitations or really remove them from your calendar, it just hides them for you. If you're sharing your calendar with anybody then they're still visible to them, and as far as I can tell that's unavoidable.

That means if you are sharing you calendar you can't use this option, since it makes it impossible to remove the events that are now spamming everybody else. You have to just manually mark them as spam every time they appear. I get an event like this maybe every other day at the moment, even though they're almost all identical and I've reported them as spam, it's unbelievably annoying. Even more annoying: gmail is actually picking up the invitation email itself as spam, so it's fully aware that it's unwanted, but then it appears in my calendar regardless. Gmail filters to delete them immediately on arrival don't seem to do anything.

I'm right back to the spam dark ages right now, it's terrible.