Advice on making a new bike purchase

[Vaultboy]

My only bike is a 12 spd alu dualsus XC bike (13.5kg), and I primarily do trail rides of 30km or less.  The n+1 itch has started and I'd really like a bike for the following:

- to go on longer rides with friends, who are primarily roadies, but who also do gravel and light singletrack rides on their hardtails. 

- to put on a trainer. (My 12 spd can't go on a trainer). 

 

My preference would be a gravel bike over a hardtail, just for a different riding experience. Also looking to spend less than 20k, because reasons. I'm currently undecided between a Rook Scout, with 8 Spd microshift (https://rookcycles.com/collections/rook-scout/products/rook-scout-groad-black-8-speed) and the new entry level alu Titan Switch (not on their website yet), which has 8spd Claris. I'm looking at these because 8 spd stuff is cheap and bombproof, and I already have a claris cassette on the trainer for my wife's 8spd bike. Swapping bikes on the trainer would be easier for her than swapping cassettes and bikes. 

A dedicated trainer bike AND a gravel bike are not on the cards. My wife's maths is that n+1 does not equal 3 (for now). 

Questions: at 13kg, the Rook is virtually identical to my dualsus bike in weight. The Rook comes standard with 47s, which will probably be plush, but will obviously not roll as fast? Will the gravel geometry, drops and slicker tyres offset the weight? Or should I go for the Titan, in which case I'm worried about the stampkar feel on a rigid aluminium -  almost everyone I know who rides alu gravel bikes have upgraded the standard 38 rubber to 43+, for more comfort.  

Anything that I'm not considering?