I would say that if you can't use the same redirection syntax as Bourne/Bash, then the syntax rules aren't "shared".

And that is because fish isn't POSIX-compliant. It's like when translating languages, some words are cognate, but some are "false friends" and while they look the same, they don't mean the same thing. So when using redirections in fish, the rules may be similar up to a point, but only up to a point.