Looking at the design history of the original battlecruisers, the Invincible class, in 1902 Admiral Fisher and Chief Naval Constructor W.H. Gard were formulating a new armored cruiser design to be more powerful than any previous. This resulted in the Minotaur class (2 x 9.2" 10 x 7.5" 23 kts, 6" armor).
Following Tsu Shima and looking at foreign developments that occured with armored cruisers in the following years the step up to the "battlecruiser" was an inevidablity. Thus, the Invincibles were really just replacements for previous armored cruisers and intended to fill the same role; that of a scouting force for the battle fleet. In fact, official documents refer to them as armored cruisers as late as 1912 when the first mention of the term "battlecruiser" appears.
If anything, the original concept of an all-big-gun armored cruiser was a mistake in retrospect. It was too much ship for too little mission. A fast battleship or a better protected less well armed cruiser would have been better paths to follow as other nations did and Jutland proved.