Even the core LineageOS and Graphine devs spend time disparaging it on reddit and twitter with comments like "It's not a very good app." and "Unfortunately Seedvault is still unreliable." Those are direct quotes.
I think it was back on LineageOS 16 that it was actually broken for the entire release. It wasn't even possible to do a basic backup at all.
Google for "site:reddit.com does seedvault even work" for dozens and dozens of examples.
why pad my opinions with outdated quotes if I can have first-hand experience? it's a good tip I gave on recent developments and your objections aren't convincing. Latest Lineage/Graphene both include in their forked seedvault repos a current enough version to check out d2d-transfer, give it another try.
I think it was back on LineageOS 16 that it was actually broken for the entire release. It wasn't even possible to do a basic backup at all.
Google for "site:reddit.com does seedvault even work" for dozens and dozens of examples.