The value of the
Bismark,
Tirpitz and the
Graf Spee would have been to divert our own heavy fleet units into convoy defence duties, rather than their war fighting power in of themselves. (as impressive as they were - the Kreigs Marine had far fewer heavy units and there was no opportunity for the huge Pacific theatre battles).
In particular for Operation Rhienburg, the mission of
Bismark and
Prinz Eugens was never to engage enemies of equal strength:
Grand Admiral Erich Raeder's orders to Admiral Günther Lütjens were that "the objective of the Bismarck is not to defeat enemies of equal strength, but to tie them down in a delaying action, while preserving her combat capacity as much as possible, so as to allow Prinz Eugen to get at the merchant ships in the convoy" and "The primary target in this operation is the enemy's merchant shipping; enemy warships will be engaged only when that objective makes it necessary and it can be done without excessive risk."
This is one of the reasons why, following the destruction of the
Hood (a battlecruiser), Lutjens never pressed the attack against the
Prince of Wales (POW - A battleship
). They probably were not aware of the issues the POW was suffering from, (malfunctioning turrets) and even if they did, the initial engagement had used up around a third of their ammunition stores. POW, even wounded and with malfunctioning turrets, would have been a much tougher nut to crack than the
Hood in terms of actually sinking her.
This is somewhat evidenced by how tough
Bismark herself was to sink -
The four British ships fired more than 2,800 shells at Bismarck, and scored more than 400 hits, but were unable to sink Bismarck by gunfire.
Bismark might have eventually won against the POW, in fact probably would have, but it would have been a pyrhic victory (in actual fact, history proved that to be the case anyway, but there was no way they could know that at this point). Their mission would be over. They would have likely sustained further damage. Their ammunition stores would have been depleted. And strategically, they would have accomplished very little - after all, we vastly outnumbered the Kreigs Marine in terms of heavy fleet units - in other words, we had plenty more BBs, and
Bismark would never have taken them all out. It was more important for them to preserve the
Bismark and
Prinz Eugens, both in terms of mission objectives and the units themselves.
Now back to the original post's point.
In many ways, the roles of
Bismark and the
Hood was reversed in intention.
Rheinburg intended
Bismark to be used as a Battlecruiser, as per Fisher's original vision:
"Heavy enough guns to destroy anything smaller, fast enough to run away from anything bigger."
Hood and POW were being used as Battleships (admttedly - that was less planned, and more a response)
, to deny the theatre to
Bismark (forcing her to run) or simply take her out.
Both
Bismark and
Hood failed in their missions. They were the wrong tools for their mission briefs. (POW did, kind of, succeed in driving
Bismark away)
Had
Bismark been a faster BC, she might have avoided engaging
Hood and POW. And evaded the subsequent hunt and been able to perform her mission. Had
Hood been a BB, or had received her upgrades, she would have been far more effective in denying the theatre, perhaps forcing
Bismark out of the area completely, or kept her moving, and unable to effectively strike, until she ran out of fuel and had to leave.
But yes, there is a certain romance to the BC, which was never afforded the opportunity to actually happen in the real world. A fast and powerful predator. She chooses her fights, and wins. Those she can't win, she's not interested in fighting.
