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I don't understand what throttle response has to do with demonstrating that it's in lockup. With an average car engine, you're going to get fairly disappointing acceleration with the torque converter locked up. I suspect that what you're seeing is the effect of having a torquey, high performance engine, based on the example cars you listed. They just don't need to drop out of lockup to deliver the day-to-day acceleration you want. Also, performance car transmissions have been tuned to behave differently than run of the mill transmissions for at least as long as I've been driving. For example, engine braking in my college friend's then-new 90s Mustang GT, whereas my family sedan would prefer to free-wheel.

Edit: by the way, I looked up the ZF8 and it's available in a bunch of configurations. One of them is a wet clutch instead of a torque converter, which I imagine has to operate like an electronically controlled manual transmission. There's even an option to have an electric motor instead of a torque converter for hybridization!