Antonyms for "more maintainable" include "less maintainable," "unstable," "unreliable," "fragile," and "complex." A less maintainable system is one that requires constant attention and upkeep, often due to its outdated design or frequent technical issues. An unstable or unreliable system may be prone to crashes or errors, making it difficult or impossible to operate effectively. A fragile system is one that is susceptible to damage or breakdowns, while a complex system may be overly intricate or difficult to modify or repair. Overall, antonyms for "more maintainable" describe systems that are burdensome, risky, and challenging to manage or improve over time.