The stock AW 8 speed transmission has been neutered by GM in order to meet strict group wide EU emissions standards and I very much doubt they devised a specific tune for the US market and removed these restrictions.
You'll understand why these cars are way off of the pace from a standing start due to the various limiters that arrive from the TCM via CAN:
Limited to to 230 PS gears 1 - 6.
Torque limited in gears 1, 3, 4, 7, 8 and as low as just 200 Nm in certain gears.
Torque limited during each gear change.
Soft top speed limiter from 140 mph.
Stop Neutral (transmission shifts to neutral at a stop for fuel economy/emissions reasons, hence the delay when you get back on the gas as that's transmission has to shift back into drive).
Without a TCM tune, you won't even see stock power or torque in most of the gears, let alone the fruits of a tune, downpipe or turbo upgrade.
I found this information by way of the German Insignia B forum, FB Insignia B group and the FB page of the German tuner EDS, who offer a very popular full TCM tune for the 8 speed but only for stock tunes or in combination with EDS own stage 2 or stage 2 +.
EDS puts 530 NM through this transmission for the Insignia Biturbo Diesel tune (stock = 200 Nm to 460 Nm) and 490 Nm for the LTG stage 2 + (stock = 200 Nm to 400 Nm).
I spoke with a Volvo tuner as the entire range uses this transmission (low and high torque versions) and they put 550 Nm through this transmission on the Biturbo diesel tunes (stock = 480 Nm) as Volvo do not use the in gear torque limiters incorporated by GM and the limiters present with each gear change are removed as part of a tune. Volvo have been using this transmission since 2012 on for example the S60 2.0T Polestar (367 PS and 470 Nm) before a tune and the tuner has not seen any problems with increased power and torque.
Hopefully of help to some of you in pursuit of those additional ponies.