Challengers of the Unknown vs. the Justice League.
The Challs had a Rogue's Gallery worthy of any super-hero---Volcano Man, Kra the alien Robot, the telekinetic Dabney, a shape-changing Multi-Man...but they were just four guys. Four nonsuperhuman guys, getting by on smarts, skill, and competence. (Same with the original Suicide Squad, for that matter.) Yet tackling foes that would give many a super-hero pause.
They seem almost quaint now, old-fashioned, as we've gotten used to superhuman battling superhuman---but like Batman, their skills more than made up for their lack of power.