Are you saying that you have the same pressure at the turbo as at the plenum? and no pressue drop?
Having a big volume of air going through those pipes with bends or reducers does affect airflow.
Especially under boost.
Although, for this application it may not be so important, i.e. 10secs at full throttle.
Think of why restrictors, aka washers, are used to control airflow in turbo cars in plenty of classes of motorsport to slow down the airflow.
also think of things like match porting exhaust manifolds or intake manifolds/plenums instead of leaving the sizes different?
2 stroke exhausts with expansion chambers are another example?
Should I continue?
Anyway, as Adrian has pointed out already, the piping runs are dictated by the space available. It's quite clear that this is the case.