> Am I naive for thinking that nothing like that should take as long as 6-9 months in the happy case and that it's absurd for it to not succeed at all?

Bluntly, yes. And so is every other reply to you that says "no this isn't naive", or "there's no reason this project shouldn't have finished". All that means is that you've not seen a truly "enterprise" codebase that may be bringing in tons of business value, but whose internals are a true human centipede of bad practices and organic tendrils of doing things the wrong way.