The phrase "art no avail" means that something has no effect or is useless. Therefore, antonyms for this phrase could include words such as useful, effective, beneficial, helpful or productive. If something is beneficial or productive, then it is likely to be successful and have a positive outcome. In contrast, if something is useless or ineffective, it is unlikely to achieve anything. Therefore, it is important to use words that communicate the exact opposite of "art no avail" in order to effectively convey the opposite meaning.