I think the first problem in this discussion is that you contradicted yourself here. You first said it was impossible to transfer the aliases, and then you later admitted it was possible.
I agree that it is impractical in your use case, considering your number of aliases (500+), but it is not impractical for every use case. I once transferred a few aliases to my friend, and it was easy, definitely not impractical at all. I also don’t mind transferring fewer than 50 aliases, and I try to keep the total number of aliases around that number. I know it would be much better if there were a way to do it in batch, but the workaround is not impractical in some cases.
The second problem is that this is a huge misunderstanding. There’s an official statement from Proton saying that they are the same on their website. To quote Proton:
Does Proton Pass use SimpleLogin by Proton?
Proton Pass uses SimpleLogin by Proton, which is an email alias service that provides advanced email forwarding. You can also manage your aliases in SimpleLogin itself.
Link: Email Aliases keep your real email address private | Proton
It’s the last question under the Frequently Asked Questions section at the end of the page