I haven't had an SMS message get lost in over a decade now. It used to happen every so often, but apparently whatever the issue was got fixed.

I have not had a problem with SMS. I think it depends on the cell phone network companies. Some are reliable. Some are not.

iMessages too. "failed to send" is a real thing, with no notification.

Messages / lets you know if it could not send a message. I do not know if these are iMessages or SMS messages, but I have seen the error message.

Yes, there's an error message, but if you close your phone, it won't notify you that it failed to send. Hours/days later, you might reopen the message thread to find the message was never sent.

Just pointing out that effectively, it is the same "problem" that SMS has with dropped messages that happens quite rarely (both are rare, actually).