Thank you for the comparison @Remah!
For my use case one remaining bit is the redirection. I found that that may be possible using permalinks.
Someone else asked a similar question: Redirect Article- possible?
It seems that if I
- move the content of one topic to the other
- delete one topic
- create a redirect for the deleted topics url to the new one
there is a redirect for anonymous users.
Thank you all for the replies! I’ll see what I make out of this for my usecase.