The antonyms for the phrase "most-well developed" would be inadequate, undeveloped, immature, underdeveloped, or uncultivated. The term "most-well developed" suggests a high level of growth, progress, and maturity in various aspects. When something is considered adequate, it suggests that it is sufficient, but not to the extent of being well-developed. Undeveloped or underdeveloped denotes a lack of progress in a specific area or overall immaturity. Uncultivated suggests a lack of refinement, sophistication or overall growth. Therefore, using any of these antonyms in place of "most-well developed" would indicate a lack of proficiency, growth, or advancement.