Nothing at all wrong with Tiagra.

I have bikes that are full Sora, 105/Ultegra mix and Ultegra/Dura-Ace mix. They all shift just fine, run quietly, and are reliable.

If anything, in winter the 9-speed is an advantage over 10-speed since the replacement chains are a whole lot cheaper. Winter is tough on chains. On the other hand, it means keeping spares in stock for both 9 and 10-speed.