Why Ibuki was not a battlecruiser

Should the Japanese Ibuki-era ships be classified as battlecruisers or large armoured cruisers?

They were large armoured cruisers; they were built before the battlecruiser concept existed.

Classification should respect the concepts available when a ship was designed. These vessels can be described as pre-dreadnought cruisers, but calling them battlecruisers retroactively implies a design category their builders did not possess. Their size does not overcome that chronological problem. The answer is a useful warning against imposing later naval terminology on earlier design intentions.