The problem isn't the SMS "protocol", but that operators still haven't been able to find an amicable solution to regulating sender names/numbers that doesn't interfer with legitimate usage, e.g. commercial businesses doing EBR texting to their customers. The problem isn't entirely comparable to that of caller ID spoofing for phone calls, and is legally and technically more complicated than you imagine.
today I got an obviously scam sms from the SAME number/source as the official ANZ sms'
SMS is a junk protocol. it just needs to be banned entirely. its got no controls or protection whatsoever.