Antonyms for the word "most high-caliber" could include terms such as low-quality, subpar, mediocre, or below average. These words describe objects or individuals that do not meet a certain level of excellence or proficiency. Conversely, if something or someone is described as high-caliber, it suggests a level of expertise, ability, or quality that is superior to most others in its category. It is important to note, however, that the antonyms of high-caliber do not necessarily indicate that something or someone is completely ineffective or useless, but rather that they do not match up to the highest attainable level of excellence.