The militias were at least as bad during the War of 1812. It is no exaggeration to say that they lost every land battle against the British, except for the Battle of New Orleans. The problem was poor leadership. Typically, the commanders of the various companies and battalions of the militia were the local mayors of governors of the States, with no military training. Only at New Orleans did they have effective leadership in Colonel Andrew Jackson.
In contrast to the militias, the American Navy was able to win virtually every engagement with the British. The American Navy had professional leadership, and was battle hardened after the Barbary wars, whereas the British had a bunch of incompetent, ossified officers who had been promoted based on their peerage.
I’d suggest that the same issues carried on into the Civil War as well. Regiments then were incorporated into the regular army, but they still had most of the characteristics of the old militia regiments. Recruiting was done locally. Most regiments contained men all from the same town. Many were organized and led by local elites (mayors, wealthy businessmen, etc.). Junior officers often were elected by the men, typically with the most popular winning election rather than the most competent leaders. Debacles like 1st Bull Run early in the war often were the result.