I disagree in that I think neither position actually gets a "the system should do this" - Devs will put together a solution they think will fulfill a user request and QA has the difficult job of figuring out why-in-the-hell the dev thinks that's something a user will figure out. /s

More seriously there is a lot of differences between the two tracks but a QA person who can write clear and repeatable reproduction steps will save a company a whole bunch of dev hours and doing so usually requires a pretty good understanding of why the system is actually breaking.