The testing HWU performed for that video was a mess. Their testing was totally inconsistent (different set of tests for each game) and they managed to convince themselves they'd at least partially refuted Battlenonsense's claims without actually testing any of those claims. Explanation of the mess below:
Recap on what Battlenonsense found:
His testing began with Overwatch. That test shows that when you reduce the GPU load via framerate capping, ultra low latency/anti-lag (ULL/AL, and I'll just use ULL for brevity) mode *adds* to input lag (He also found that when GPU-limited, ULL reduces input lag as advertised).
He then uses PUBG and BFV to confirm this finding. To do this, he compares input lag *with ULL off* when GPU-limited vs. when not GPU-limited.
In all cases, Battlenonsese uses in-game FPS capping. He does not use RTSS for his testing. So in addition to the RTSS claims being false as RealNC explained, they're irrelevant. In other words, HWU is so off-base that they're not even wrong
Recap of HWU's testing
For Gears 5, HWU tests the following scenarios:
no FPS cap, ULL off
no FPS cap, ULL on
in-game 144 fps cap, ULL off
in-game 144 fps cap, ULL on
RTSS 144 fps cap, ULL off
RTSS 144 fps cap, ULL on
This test shows that in Gears 5:
-an in-game FPS cap reduces input latency
-an RTSS cap does not reduce input latency
This test does not tell us anything about the effect of ULL. Gears 5 runs on DX12, which is not compatible with ULL. This is the only time HWU runs the correct set of tests and
actually hits 99% GPU usage, but because it's a DX12 title their results are virtually useless.
HWU then changes things up, testing an appropriate game (BFV) but changing his methodology so that we can learn nothing about Battlenonsense's finding that ULL-on is inferior (in terms of input latency) to ULL-off when not GPU-limited.
no FPS cap, ULL off
no FPS cap, ULL on
no FPS cap, ULL on, future frame rendering off
in-game 120 fps cap, ULL on, future frame rendering off
RTSS 120 fps cap, ULL on, future frame rendering off
These tests do not tell us anything about the effect of ULL (he leaves ULL on for all tests except the first uncapped scenario). They also don't really tell us much about the effect of using frame capping to go from GPU-limited to non-GPU-limited, as he only hits 97% max (this is the upper end of the utilization range where Battlenonsense found the benefits to input latency begin).
For Far Cry 5, HWU's tests a "GPU-limited" scenario where GPU utilization is at 92% max. In the in the voiceover, they even acknowledge that they're not testing a GPU-bound scenario at all. Remember, Battlenonsense's Overwatch testing found the reduction in input latency was achieved by limiting the GPU load to 94-97%. So the 4-5 ms increase in input latency that HWU found when using an FPS cap doesn't actually tell us anything
about the effect on input latency when GPU-limited vs. not GPU-limited. And again, since he was never GPU-limited, this tells us nothing about ULL other than providing another confirmation that ULL doesn't reduce input latency when you are not GPU-limited.
HWU's Divison 2 testing again tells us nothing about differences between GPU-limited and non-GPU-limited scenarios or ULL (I don't think he specifies, but I think he's testing in DX12, which doesn't support ULL. Either way, ULL is not included in this testing). The uncapped scenario only hits 97% GPU utilization, which is again within the range where Battlenonsesne reports you start to get improvements in latency by turning ULL off. All HWU has shown is that when not GPU-limited, higher FPS generally results in less latency.
Metro Exodus testing is the same story as the Divison 2's testing. No ULL as it's DX12 and max GPU utiliztion is only 95%.
CSGO - he only tests with ULL on. Again, all this shows is that when you leave ULL on, higher fps generally results in less latency. If he had tested ULL on vs ULL off at each frame cap and frame capping method, we could have learned something useful.
Fortnite testing - again, HWU's testing is never GPU-limited (max utilization is 94%). He has yet again shown that when you leave ULL on, higher fps generally results in less latency.