Mission design separates battlecruisers from battleships

If the BC-304 can fight the setting's largest warships, why is it a battlecruiser rather than a battleship?

Classification follows intended role, not raw power: it is a fast strike and cruising platform, while a battleship would be optimized to stand in the battle line.

A ship that can survive a battle is different from one designed primarily to fight in the battle line. A true defensive battleship would trade some hyperdrive performance and general-purpose space for heavier armor, shielding, and weapons. The BC-304 instead combines long-range strike, cruising duties, speed, and broad utility; later Asgard weapons create an advantage without changing its original purpose. Its relative place in the setting resembles a third- or fourth-rate ship operating where no dedicated first-rate equivalent exists. HMS Hood illustrates the battlecruiser logic: overwhelming power against most opponents plus the speed to refuse an unfavorable engagement.