Plus, the numbers in that video are off.
A/D > D/A latency on Helix Floor/LT/Rack is 1.8 ms. In part because of its third DSP/coprocessor, Stadium is indeed slightly longer at 2.25 ms.
Agoura amps add a tiny bit more latency than HX amps (due to how impedance curves are implemented) but it completely depends on the amp. For example, we're measuring 2.5 ms with the HiWatt and the HiWatt's matching cab. The video doesn't mention which amp is used but FWIU, none push up to 3 ms.
Cabs don't add any latency, nor do user IRs unless empty samples are added at the beginning to ensure they're phase-locked with others in the bundle (which I understand is fairly common?).
One competitive product hits 4 ms with a single drive, amp, and cab (according to their own specs) and no one seems to complain.