Why Constitution was not an age-of-sail battlecruiser

Where would heavy frigates such as USS Constitution sit on a battlecruiser spectrum?

They remain cruisers in this comparison. The operational role of 64-gun ships provides the closer age-of-sail analogy to battlecruisers.

USS Constitution and similar heavy frigates belong on the cruiser side of the comparison. The closer operational analogy to a battlecruiser is a 64-gun ship such as Agamemnon or Africa, considered alongside the larger 74- and 80-gun ships. A heavy frigate meeting a 64-gun ship would need to get away. Comparisons with 8-inch and 9.2-inch cruisers, Deutschland and Alaska emphasize the heavy frigate's strength within its own category. An Alaska facing an Iowa supplies the final example of a powerful cruiser being badly overmatched by a capital ship.