Why Arctic convoys still needed heavy cover

Could Arctic convoy escorts have overwhelmed Tirpitz with aircraft and shells alone?

Possibly, but naval commanders preferred overwhelming combined force, including battleships, so a German sortie could not exploit a failure or gap in the air attack.

Aircraft, cruisers, and destroyers could impose severe risks on a German sortie, but convoy commanders preferred to have battleships available as well. The Battle of North Cape shows the logic: cruisers and destroyers fought Scharnhorst, while HMS Duke of York ensured that heavier force was ready. The final operation against Yamato similarly used carrier aircraft with battleships available behind them if the air attack failed. Layering those forces reduced the chance that one missed attack or local reverse would expose the convoy. The aim was to bring overwhelming force rather than accept a fair fight with Tirpitz or Scharnhorst.