Kettlebells differ from barbells because a kettlebell is a compact offset weight held by a handle, while a barbell is a long shared bar designed for stable, heavy loading. That changes movement path, balance, grip, setup, and the kinds of exercises each tool handles best.
Kettlebells are usually stronger for swings, carries, goblet work, compact conditioning, and skillful offset-load movements. Barbells are usually stronger for heavy squats, deadlifts, bench presses, overhead presses, and standardized strength progression.