First off all the british actually built battleships worth roughly 39.000 tons and the Hood was at a tonnage of roughly 41.500 Tons also the Vanguard commissioned in 1946 was at over 50.000 tons, thus beating the Bismarck
Also at the time of operation Rheinübung had the wast majority of the Royal Navy intact, at September 1st 1939 the Royal navy consisted of
11 Carriers
17 Heavy armored ships (BB and BC's)
76 Cruisers (both CA and CL)
243 Destroyers
Although the fleet the Royal navy had in the hunt was roughly 100 the number of ships that Bismarck faced (and fought) in the final battle was much much less
2 Battleships (Rodney and King George) and 2 Cruisers (Dorsetshire and Norfolk)
Also while we're at this a single hit from Rodney's 16" guns knocked out both Bismarcks front 38cm turrets, also a 8" shell hit from Norfolk destroyed the main command tower and soon after the main director position was destroyed, those are BTW some of the very heavely armored parts of the ship
Also if we look at the angeling of the british cannons you'd notice one small problem in sinking the ship, the minimum angle of the british ship's cannons makes it practically impossible to make underwater hits on the Bismarck practically making it impossible to actually sink it!
Also all searches of the wreck have either turned out noting or very unlear results, mostly indicating that the ship had suffered fatal damage, this and the very few survivors (and no senior crew members) makes it very hard to prove or disprove anything, it's a fact though that within 12 minutes of the opening salvo the ship was practically lost, having lost both front turrets and the main director position
All this makes it very hard to judge, but in my oppinion if the british battleships had been positioned properly they could propably inflict severe underwater damage, the above surface damage indicate that if they had scored underwater hits they would have sunk Bismarck quite easely even