This is not a matter of not having enough exhaust energy to run the turbo. You, I, we don't know that, unless you ask the person that was doing the dyno.
But, there is a threshold that turbo needs to get up to spool and before that threshold a turbo will generate a of boost exponentially to its input. Once that threshold is passed it will "spool up", but before that a turbo will not simply sit there not create any boost and make the engine not have any power. Maybe if you run something like 6-7:1 CR, the low compression is going to make the car powerless until the turbo spools.
But its a stock 2.5L V6 engine, a 6-7:1 CR would have much less horsepower so it can't be that and if it was at WOT you would have seen a power curve similar to one looks like without a turbo.
Here, take a look at this wild Supra...
http://www.walserrz.com/dynos.html Look at the last dyno sheet, see that little flat line right before the the chart flys up and make tons of HP. Same thing, leave a car on the dyno and don't give it any gas you will get nothing but a flatline...
Here's a theory and a little explanation of whats going on. In the red you see nothing but a flat line because the throttle has been closed, at that point the ECU has gone into a close loop mode and is starting to lean out as part of its standard programming (trying running your car at 55mph and let go of the gas, you will see injectors and a/f ratio goto 0).
The Yellow, its a common trick to run it really rich in the lower RPMs to get a turbo spooling. You can see this as it reaches 13:1 Its a bandaide but it works...
In the green the turbo is spooling and you adjust the A/F mixture to get the desired EGTs. If there was a tuning problems they usually show up as spikes or power dips, somtimes the dyno plot is a squiggly line which I don't really see.
Its a little phoenemon called starting to record the dyno before you give it gas.
