It seems that you have mistaken the Dynamic Force engines for regular undersquare engines. But they aren't. Dynamic Force is a piece of engineering marvel since it combines so many favorable chracteristics into one package without the usual compromise.
Usually an undersquare engine trades low end torque for high rpm, which means less specific power (hp/L) but better efficiency and driveability in normal driving conditions. That's why they are not known for performance. The GR and UR series were optimised for high specific power (first on the market to have more than 80hp/L), therefore they are both heavily oversquare to squeeze out as much rpm as possible. Do note here the discussion is about civilian engines without exotic internals: sports car engines can rev over 8000rpm because of forged components that are impractical to produce on a massive scale.
Dynamic Force does not have this compromise. The A25A-FKS has a bore of 87.5mm and a stroke of 103.4mm (for a bore/stroke ratio of 0.846). It almost looks like a truck engine, but it is nothing like a truck engine. The peak power is 205hp@6600rpm, and the peak torque is 250Nm@5000rpm. 82hp/L on such an undersquare design is very impressive, especially considering it does so while achieving more than 40% thermodynamic efficiency. Usually manufacturers set the red line at 200rpm above peak power, so this engine can rev up to 6800rpm. There simply aren't many truck engines that can rev this high. And you also have to consider with such a long stroke the mean piston velocity is 23.4 m/s, which is in the realm of most performance engines out there, yet the A25A does not use forged internals. 82hp/L, 40% thermal efficiency, 23.4m/s mean piston speed with regular internals, you cannot find ANY engine in the entire industry that can do all these things at once.
But you may ask, if it's so undersquare, why is torque so low? That's VVT-iW at work. At low rpm the engine operates in Atkinson mode so torque is very poor, but the undersquare design mitigates that to some extent. If you examine the full torque curve of the A25A you will also notice there is a significant torque dip during Atkinson-Otto cycle transition. This is where the complexity of this engine stops. The perfect solution here is to use continuous variable valve lift to smooth out that dip, and TMC does have that technology (Valvematic). But maybe it's not worth the added complexity and reliability concerns. Still the torque curve is way better than the previous 2AR-FE/FSE engines. The lack of low end torque can be easily rectified by turbocharging or hybridzation, so no concerns for performance cars.