too weak to stand competition 不堪一击

“不堪一击”，汉语成语，字面意思是力量薄弱，经不起一击（cannot withstand a single blow），形容十分脆弱，或经不起反驳。可以翻译为“too weak to stand competition [attack]，very vulnerable或 (of a theory) that cannot be defended against attack or criticism”等。

例句：

不堪一击的理论

Untenable theory

这些土匪是一群乌合之众，不堪一击。

These bandits are just a disorderly mob and will collapse at the first blow.