Most destroyers and frigates built since 80s have had only one main gun. In the Daring’s case, it’s a 114mm gun, which is not terribly small compared to the 127mm guns used by the USN.
Like a lot of British projects, the Daring has been built with space for, but not with add-on weaponry due to funding issues. So it’s anti-sub capability is mostly provided by its helicopter.
There are plans in the pipeline to upgrade the guns to 6.1 inch (155mm) weapons to bring it in line with the army’s self-propelled artillery pieces. But yeah, its pretty crap. Expensive crap too, £1.1 Billion a ship. We’d have been better off buying US Aegis ships. Apart from maybe a slightly better radar, this ship is a donkey, whose primary virtue is providing jobs for British engineers.
Like I said in an earlier thread, perhaps we’d have been better buying American, and ploughing all that money into a British space program instead...