I agree. The reason that guy did it in his golf 1.4TSI is because hes running a GT30+ turbo aiming for 500Hp. Obviously that is going to require some substantial air flow.
With the stock or even the LO270 you wont need anything as extreme as this and the gains would be negligible.
Most people seem to think that the supercharger operates all the way until 3500rpm when in reality it doesnt. It operates until the turbo is on boost then disengages completely and when logged i've seen that the supercharger disengaging on mine as early as 2500rpm as the turbo is already on song and on boost. This is why pulley upgrades and supercharger upgrades are pointless.
So consider when driving how likely you are to be in the 2500-3000rpm power band when driving spiritedly? Not very often id imagine, and in reality its not wise to go WOT at those sort of revs in higher gears as its not healthy for the transmission and clutches as you expose them to the peak torque for a prolonged period. Its better for your transmission and ultimately performance to change down a cog or two, use the power instead and protect your transmission.
Dosent say that the supercharger disengages as soon as turbo is on boost in that technical pdf. It talks of the changeover. By saying on boost do you mean 19psi where it stays until it tails off. (typical stage2 map) is the peak boost of 22psi all supercharger then without the turbo wastegate closed?
I was thinking along the lines of 1/4mile performance with this mod as like you said one wouldn't be in that rpm range often.
I think the way forward in tuning this engine isn't about power, if your aiming for 1/4 mile times, its about making the power you have as deliverable as possible and making things as efficient as possible. Im only aiming for 250.