Did nothing, as in, didn't cool the air charge at all, or simply didn't outperform an air-to-air intercooler?
Is that a mathematical evaluation, or a physical trial?
Liquids are inherently more dense, and thus more capable of thermal transfer... so surface area becomes a factor.
Even if the liquid intercooler is designed to be only as effective as absolutely necessary, and doesn't outperform an air-to-air unit, in terms of thermal transfer capacity... it doesn't take into account several other factors.
Size - a liquid intercooler is likely a much smaller and more compact core because the liquid can transfer more thermal energy per square inch of core surface area than cooling air. An equivalent or better air-to-air would have to be a larger core with more transfer surface area.
Airflow - an air-to-air intercooler requires fresh airflow in and out, and an engine bay is not exactly an easy place for that to occur, especially without hood scoops, fender vents, or other more complex airflow management, and heat soak shielding.
If you move the intercooler core to an area with fresh airflow, such as the front grille, it creates more considerations.
-safety regulations for front impact
-increased costs for more parts
-packaging and routing around other components
-charge air volume between the turbocharger compressor and the intake valves and vacuum/pressure management.
-air metering for AFR over time.
A shorter intake tract, and less volume creates faster throttle and turbo response, more accurate metering, fewer parts, fewer joints and points of failure. It is easier to route smaller diameter liquid coolant piping with a pump, than ducting charge air, or fresh air around the engine bay.
The chances of a charge cooler leaking coolant into the intake tract are probably significantly lower than the risk of the radiator other fluid coolers rupturing and dumping their contents on the ground outside of the engine... those coolers are more subject to debris impact than a filtered air supply... and foreign object damage to the charge cooler(s) is likely to include bits of compressor debris from the turbos taking damage first.
Spontaneous component failure is a possibility... but there are thousands of component parts on a production car. "You spends yer money, and takes yer chances" with the whole system.
They also have to balance ultimate effectiveness against durability, warranty liability, packaging, federalization, fuel economy standards, subcontractor production, R&D, and the cost of the vehicle overall to produce and the customer's ability and willingness to pay the price.
Think of all the manufacturers that are producing turbocharged engines these days, and how many of them have liquid charge coolers, from F150 EcoBoost V6s to McLaren SpeedTail, and every price point in between, in volumes of tens of units of hypercars, to hundreds of thousands of mainstream vehicles.... the instances of failures en-masse are very low... and if so, are either warranty or recall covered for repair or preventative replacement.
Sure, the aftermarket may be more effective, they have less restrictions, and a customer base willing to spend a significant amount of money above and beyond the price of the car they bought.
Sure, Nissan may be able to do a bit more R&D to optimize the VR30DDTT incrementally and improve things a bit while they are working up the Z, and interested in making it well-received, effective, and reliable when it comes out.
They can also see what happens when costs increase, and Supra costs a significant amount more money, and is not selling like gangbusters.
Sometimes car companies make boneheaded choices to cut costs... other times they are making things possible that would otherwise not be feasible, and would otherwise not happen, or not succeed.