Battlecruisers are remembered for being misused in combat, I think. They were sent up against Dreadnoughts and got blasted because line tactics didn’t allow them to make proper use of speed, which was their main defensive advantage.
If by tank destroyers he means assault guns or other tracked guns like the S-Tank, then yes, I’d call them disappointing in the long run, as they could be easily outmaneuvered by newer generations of faster, better armored turreted tanks. Taken for what they were, though – cheap ways of getting armored firepower into combat on a short schedule – I think they did okay in their own brief time. They were rapidly rendered obsolete by guided missiles, though.