As noted, Chaz"l felt this verse referred to Ahm Yisroel in conquering the land in Y'hoshua's time. Let's remember that ALL of Israel was involved in the enterprise with a level of unity.

Although we have shown that we can and will fight as lions, there are 2 conditions that aren't present as in Y'hoshua's time =>1.all of Israel (not even a majority) is NOT involved, and,2.sadly enough,there surely isnot enough unity.

Everybody knows the famous comparison of Kings Akh'av and Chizkiyahu where the former spread idolatry throughout the land and was victorious in battle and the latter spread Torah throughout the land and fell to Sancheiriv. Chaz"l tell us of the great unity of Ahm Yisroel, despite the idolatry, during Akh'av's reign;hence the victories in battle. However,during Chizkiyahu's reign, despite the great torah knowledge of even the youngest children, there was great division spread through the bad graces of lashon hara and consequentally,they were vanquished.