Why not have a secondary ship assigned to the same area that we can get to know when an extra ship is needed? It works great in Vanguard. Why box yourself in?
Since when do the novels box themselves in? Only in your imagination.
Every ST novel has introduced new ships, planets and/or new personnel, but this is ST and, in the main, it is
expected by the buyers of licensed fiction that they will be able to read about characters they already know from canon. By your logic, the minute that new ship is reintroduced in another novel, the writer has committed Small Universe Syndrome, so you're advocating that the novels spend lots of time telling us about great new characters we are doomed never to see again?
"New Frontier" had some new-to-fiction characters but, IIRC, Paramount insisted on some familiar canonical faces to join them, so PAD specifically asked for his TNG guest actress favourites, on a promise that the canon had probably finished with them: Shelby, Selar, Lefler. Similarly, "Titan" reintroduced DS9's Melora the Elaysian, based on a character concept the show was unable to use as a regular. SCE added Scotty and reintroduced Sonya Gomez and a pair of Bynars. The DS9 Relaunch has reintroduced Ro and Opaka, among others.
And they
do.
But there is also storytelling potential in having two known (to us) characters meeting up and learning to work together. Again, you seem to be advocating that the novels spend lots of time telling us about great new characters we won't ever to see again.
Titan has a crew made up of all sorts of races that we know little about and have never crewed a starship together before.
And that's precisely what
every "Titan" novel has brought us.