See what Habs Fan said.
Why do you keep resisting any explanation for anything? It seems as if you're not interested in giving the series any type of benefit of the doubt at all. You're too quick to say "It doesn't work". As a Disco Fan, I'd think you'd want to figure out a way to make it work, and then only say it doesn't work as a last resort instead of a first resort. Personally, if I say something doesn't work, it's because I exhausted all the other alternatives first.
Besides that: geometry. 51,000 light years from wherever the Enterprise is can lead to anywhere. It doesn't have to be Terralysium at all. It just has to be 51,000 light years away and in the Beta Quadrant. Spock has faith that wherever they located the signal, it was from Discovery. And faith is one of the themes of the season, so it's a fitting way to end it.
Liking something doesn't mean that you stop acknowledging its flaws.