Well that's the thing, aside from the half a point difference in compression ratio (which to be fair should be made up for by the longer stroke of the YB), there's no inbuilt reason to the engine design that should make the YB feel lazy and unresponsive compared to the other engine.

Which makes me wonder, as mentioned, if it's the old L6 ECU/TPS etc, and the heavy ass YB flywheel.

The flywheel will prob help the lack of revvyness I mentioned. I mean on boost it's never going to rev as freely as it's less powerful than the other engine, but in general, off boost, part throttle, etc, even out of gear, it's much less willing to rev.

Confusing really, as the difference is absolutely massive, despite the YB having the turbo that boosts sooner. As you say, it ruins the experience when you drive them back to back. At the same power level the YB would be ten times more fun if it wasn't for this.

I honestly don't think it's a YB engine thing, I think it's something that can be sorted. Not 100% how though, hopefully someone does. The rally guys etc might be the best to know as it's the things they'd want for rallying.