The true value of the bonus action attack comes not in its base weapon damage, but in its ability to increase the chance of you getting at least one hit per turn. In 5e, there are many valuable damage-dealing abilities contingent on a hit, regardless of whether that hit is an action or a bonus action.
These abilities include: Hunter’s Mark (Ranger), Divine Smite (Paladin), Rage Damage (Barbarian) and Sneak Attack (Rogue). Additional subclass features; Hexblade’s Curse (The Hexblade Warlock) and Psychic Blades (College of Whispers Bard), for instance, also benefit from any chance to hit.