[Izkata]

I can't answer the mRNA half (because they're brand new and we just don't have that data yet), but I'm pretty sure I know where the "infection does not create long-lasting immunity" side came from:

Around 9-12 months ago, a study came out that said antibodies from infection last 3 months. They couldn't say any longer though because that study only had 3 months of data. Unfortunately, this was largely reported on as "up to 3 months", making a lot of people think immunity only lasted a maximum of 3 months.

Since then, now that we have more data, further studies have come up that keep extending that duration. Last I recall I think there was one that got to "at least 14 months"..? But these ones don't get as much spread as the original wrong reporting, so it got kinda stuck as "don't create long-lasting immunity".