Given the amount of SMS spam and the lack of such on iMessage, I am, at this point, ready for iMessage-only life. The few friends I had who were not iPhone users, I gifted them iPhones. So far none switched back, and I get to ignore all non-iMessage incoming messages (and thus 100% of SMS spam)
Does iOS not have spam blocking in the SMS app? It all goes straight to the spam folder in Google Messages, haven't seen a spam SMS in years.
iOS has features for SMS spam blocking, but all of the proactive ones require the user opt-in (not enabled-by-default).
There are 3rd party block list apps, there is an OS setting to trust the filtering of your cell provider, and you can report the sender/content of a message directly to Apple for the first message from a new sender.