If the Bismark and Prinz Eugen hadn't split up both would have ended up sunk. A single battleship (and not all that powerful of one to begin with) and a single heavy cruiser stood no chance of success in a stand up fight with what the British had in the Atlantic to take them on with.
In Bismark's final battle the Rodney (9 x 16") and KGV (10 x 14") totally overpowered the Bismark. The numerous heavy and light cruisers (along with dozens of destroyers not to mention aircraft carriers) just overwhelmed the Bismark and would have done the same to the Prinz Eugen.
Adding two or three destroyers does nothing to change this equation. U-boats are useless as part of such a task force as they could barely keep up on the surface and could not coordinate their attacks if submerged.
This is why every nation didn't operate submarines as part of surface task forces but rather independently as pickets or in Guerre de Course campaigns against merchant shipping.
That the Bismark (or Prinz Eugen) sank the Hood was meerly a stroke of luck that wasn't likely to be repeated the next time they ran into several British capital ships (as acutally happened).