Are you aware that many large fish use gliding as a form of energy conservation. This is facilitated by pectoral fins. They can still possess swim bladders. Within the tuna family there are species with and without swim bladders. Indeed the albacore tuna with exceptionally long pectorals has lost it and relies on dynamic lift. Others such as the bluefin and yellowfin use a mixture of dynamic lift and buoyancy adjustment from their swim bladder. These fish are incredibly active but still find benefit in not relying solely on dynamic lift. Also unless the lift force acts through the centre of mass there will be a resultant moment causing a rotation. In sharks this could be the reason for the larger upper lobe on the tail which these fish seem to lack? My suggestion is that the larger pectoral fins could provide a means to balance the changes in hydrodynamic lift resulting from the changes of mouth open and mouth closed conditions?