I like Alfonso, but that excuse was a bit....ehhhh.....
The Z34 with 332hp was offered completely topless.
And T-Bar roofs can absolutely be engineered to perform nearly as well as a solid roof.
However, it's a dated design. Not everyone at Nissan remembers mullets and gold chains. I think Z owners would enthusiastically like T-Tops though.....
Nissan probably had some internal turmoil going on during this car's development, I would guess Nissan was marginalizing Ghosn at this time (that's why so many new Nissan designs are leaps and bounds better) and they had a lot on their plate.
They need to get the new Z out sooner than later, the curtain of regulations is closing on these cars.
I will add, the T-Tops on my Datsuns/Nissans always worked well.
One of the features I miss from the 90's cars are the T-Tops and Targas. The Z34 came in a convertible, so they could've done it here. It would come at the cost of weight though, and the car is heavy enough as is.
The Supra is another, and probably even bigger offender. Its chassis is designed for a roadster right from the get go. In fact is the only dedicated sports car chassis BMW makes. Toyota even had a SEMA car made with a Targa and big wing. They know, these car makers just half-fast everything anymore. Or they hire "new youthful" people out of college that really don't pay attention to history, or care to.