People complain about the rain in Belgium too; Brussels is indeed wetter than Belfast in April, May and June, but otherwise Belfast wins - and even in April, May and June, Belfast has more rainy days; more ongoing drizzle and damp than short sharp showers.
I am a bit sceptical about the numbers given for average sunshine hours per day in each month, especially for December. I can just about believe that Brussels gets 5. It seems a bit harsh to say that Belfast gets none. And it is physically impossible that Birmingham should get 11!