Interestingly, when Wellington was not in command of a British army, the operations usually resulted in failure. Flanders in 1793-1795, Holland in 1799, the two 'expeditions' to Buenos Aires, Spain in 1808, Eastern Spain against Suchet, Holland in 1799, and Bergen-op-Zoom in 1814 were all failures-not to mention North America in 1814 (Plattsburg, Baltimore, New Orleans and the Niagara frontier). Without Wellington the record of the British army during the period would indeed be dismal
Of course - Britain was primarily a naval and trading power and in these areas Britain's contribution was crucial in defeating Napoleon.
Britain's army was small in this period and could not take the leading role in land operations. In characterising the performance of the British army as "dismal" you don't mention the successes of the army (for example Egypt and Maida - both won without Wellington), the campaigns in India (in the early years without Wellington) and the capture of French colonies.