You really need to ask yourself “what do I need?” as opposed to “what do the marketing guys tell me I need?”
For a winter commuter / training bike I personally wouldn’t go for a carbon frame. Something like a Whyte Charing Cross if you are edging towards the cyclocross side of things which the Diverge is aimed at, or a Cannondale CAADX would be my recommendation. Anything with Tiagra / 105 and BB5/BB7 brakes would be ideal, and if you look around you could easily get something for around £1,000 brand new. Tiagra and 105 kit works well and is cheap enough for you to replace at the end of winter when its all rusty and knackered, and even then you’ll probably only need a new chain and cassette. The shifters will go forever with little attention.
If you really want carbon then an On-One Dirty Disco would be hard to beat on price, but as far as I’m aware the latest build only comes with SRAM Rival kit.
If you want something more racy then you can’t go wrong with that Giant Defy, but again, anything over £1k for a winter bike seems excessive unless you are competing.