No I don't have data to back it up. I say this because I vaguely recall reading somewhere that the reason why apple/google cooperation broke down was because apple insisted on banning spammers and google didn't want to. I have no idea where I saw that other than it was mentioned in a HN comment somewhere.

I remember that it made sense and seemed plausible to me at the time because I've also actually never received a spam iMessage in my whole life. It never even occurred to me in that moment this was the case until I read that comment and was like, "O yeah, right, I've actually never gotten spam on iMessage come to think of it." I just assumed that to spend spam via iMessage required apple hardware or that for one reason or another it just wasn't very viable.

On the other hand, I have gotten a lot of sms spam in the past, and I continue to get spam on WhatsApp.

As a side note, my sms spam has decreased dramatically after I ported my mobile number to google voice vs. when my carrier was T-Mobile. It's anecdotal but still telling.

There are people in this discussion posting opposite experiences from you, so it's probably all anecdata either way. But I think it's a convincing argument that SMS is significantly more vulnerable to spam because the price of entry is negligible and it lacks the traceability that comes with a requirement to have an Apple ID to use iMessage.

I hope you're reporting the spam you get to Apple, because the fastest way to stop it is to have the offending account terminated.