Yup, that's the policy. I could find it on Matrix if you like, but basically the main dev isn't interested in spending the time for backwards compatibility, and nobody has yet stepped up.
So it's not like anyone is opposed. Priority right now is improving supporting new lemmy versions, followed by high priority bugs and features.
Plus it's been a few pretty hectic weeks for the devs. It's absolutely understandable there would be issues with this huge influx of new users and scramble to fix issues.
Yeah development speed should slow down in the future. Right now I understand the move away from websockets became really urgent to support all users. And now that's completed.
Next urgent thing is captcha I guess but that doesn't sound like a massive addition at least.
Customarily, backwards compatibility starts with version 1.x, so until Lemmy doesn't release a 1.x stable version, instead staying on a 0.x "let's break everything", backwards compatibility is more of a lucky coincidence.