Why Britain did not rely on bombs alone at Taranto

Would Taranto have worked better as a bombs-only attack followed by torpedoes after the Italian fleet sailed?

No. The Fleet Air Arm distrusted its bomb quality and planned around torpedoes as the reliable battleship-disabling weapon.

The proposed tactic is to damage topsides with bombs, lure the Italian fleet to sea, and use torpedoes in a later strike. British planners lacked confidence in the available bombs because their construction and quality control were poor. The Fleet Air Arm trusted torpedoes to produce disabling underwater damage. The original two-carrier concepts already expected thirty to thirty-six Swordfish and debated using Fulmars for supporting tasks. Planners therefore built the operation around a larger torpedo attack rather than gambling the raid's main effect on unreliable bombs.