Correct.
For example. Lets say your ecu requests 20 psi. The stock intercooler has a 2-2.5 psi drop roughly (based on limited data). That means for your boost target (it's actually a torque target, but this is just an example) to hit 20, the turbo has to produce 22-22.5 psi)
If the replacement intercooler has a 1 psi drop (vs the 2.5 of stock), now the car only has to produce 21 psi to hit that target. (Turbo has to work less hard).
This also mean it reaches targeted boost faster.
So though there would be some lag due to the increase in intercooler volume..
1) It either isn't large enough to be bigger then our drive by wire lag
2) The pressure drop reduction compensates for it enough that it is largely unnoticed.
Keep in mind when reading reviews and comparisons of intercoolers to compare the data and find out which mods the owners are using.
For example, APR recently went on an optimization of some of the stage 3 cars, remedying the reasons why they weren't reaching power targets. The reasons? aftermarket bov, aftermarket throttle pipes, aftermarket charge pipes.
So if one guy with a wagner is reporting lag, and one isn't, compare their mods. One guy might have a bunch of aftermarket charge pipes leaking boost all over the place. (The OEM piping flows fine, and stock dv holds fine at stage 3 levels (540 bhp))
I particularly like the IE intercooler because of its design, and because it comes with new hoses. If you were really worried about size effecting you, the unitronic is smaller, but I feel that is more sized for an IS20, not the IS38. (APR/IE).
