The antonyms for the word "more ill founded" would be "well founded", "legitimate", "valid", "sound", "justified", "logical", "reasonable", "sensible", "reliable", "authentic", "truthful", and "fact-based". These words imply that something is based on evidence and is worthy of trust and confidence. In contrast, "more ill founded" suggests that something is not supported by evidence, lacks logic or reason, and should not be trusted. Using antonyms when describing something can help communicate a clearer message and provide a more accurate description of a situation or argument.