Is preserving the Grand Fleet the strongest objection?

Is preserving the intact Royal Navy the strongest argument against the Baltic operation?

Yes. An intact Royal Navy makes British defeat unlikely, so the Baltic gamble must justify risking the country's central strategic guarantee to meet its Entente commitments.

An intact Grand Fleet is Britain's strongest insurance against defeat, so risking it in the Baltic jeopardizes the foundation of British strategy. The operation tries to shorten a continental war by staking the force that makes a German victory at sea unlikely. Britain's commitments to the Entente still require it to account for France and Russia rather than wait safely behind the fleet. The counterfactual must therefore justify exchanging a reliable strategic guarantee for a possible early victory.