I agree to a large extent that the League of Nations had so many weaknesses that it was doomed to failure.
The membership turned out to be the major weakness of the League of Nations. As three of the great powers, which were Germany, the USA and Russia were not the members of the League. Germany was not allowed to join as it was a defeat nations and Russia was not a member as the western nations refused to recognize its communist state. While the United States refused to join as it was following a policy of isolationism, which was a policy of not getting involved in other countries' problems. The membership was predominantly European and this was a further weakness. In Asia, the League of Nations was associated with white supremacy and colonialism. Although Japan was a permanent member of council, the league refused to agree to a resolution, which declared that all races were equal.
Besides the membership problem, the League did not have the strength to force major powers to accept rulings. It had no army and no police force. If a country were found to have acted against the principles of the league, the league members would apply economic sanction against it. However, this harmed their economies.
Despite of all its weaknesses, the League of Nations also played an important part in the outbreak of World War II.