While the pension seems small, keep in mind that it was in addition to either regular pay or half-pay. It does not appear to have stopped. If the pension was accumulative with additional grants for multiple wounds it could run to a nice sum of money.
Take the example of Charles Napier.
At the battle of Corunna, he was five times wounded: his leg was broken by a musket shot, he received a sabre cut on the head, a bayonet wound in the back, severe contusions from the butt end of a musket, and his ribs were broken by a gunshot
At the battle of Busaco he was shot through the face, his jaw broken, and his eye injured. He was sent to Lisbon, where he was laid up for some months.
He had the small non-resident and sinecure government of the Virgin Isles conferred on him, in consideration of his wounds and services, and he held it for a year or two; but when pensions for wounds were granted he resigned it.
He went on further active service even with the pension award. Napier went to Guernsey in January 1812 in command of his regiment. In May 1813 he was appointed to command a brigade to take part in the expedition in the Chesapeake and various minor operations on the U. S. coast during the War of 1812. Anxious to serve again in the Peninsula, he exchanged back into the 50th Regiment. He sailed for England in September 1813 and arrived to find the war with France concluded. He served with the 50th regiment until December 1814, when he was placed by reduction on half-pay. In May 1819 he was appointed an inspecting field officer in the Ionian Islands. Later commanded in Northern England, conquered Sind and became CinC of India.
I imagine that the government considered that most officers had an outside source of income and that the pension was a supplement. The Royal Veteran Battalions and perhaps the Garrison Battalions were available for disabled officers and there were any number of Fort Government and staff positions available.
In 1810 the annual rate of pension for Regimental Officer's Widows was:
Colonel £80; Lieutenant Colonel £60; Major £50; Captain £40; First Lieutenant £30; Second Lieutenant, Cornet and Ensign £26; Paymster, Adjutant and Surgeon £30; Quarter-Master and Assistant Surgeon £26; Veterinary Surgeon and Chaplain £20.