In the Source engine and for many other shooters, A+D and W+S do not result in a null input, they are two registered inputs that by engine and game design cancel each other out and result in a null output.
It is as you say in that 1 and -1 result in 0, but this is done in the game’s movement code, intentionally, to force players to learn to only press one of the two opposing keys at once, as a skill.
Theres a reason many pc FPS players consider the source engine to be the gold standard for control responsiveness and player movement design/feel, and this is one of them.
Its not from an inability of the game or engine to handle too many inputs.
Also I am fairly sure the macro set up you are describing to allow for the strafe cancelling is a null bind, which Valve has also banned.
Either way, you are not understanding the entire concept of intelligent, dynamically sensitive key switches in the keyboard itself, resulting in dramatically (for a twitch shooter) decreased reaction times from the same actions done on a different keyboard…
This is different than just setting your mouse dpi to be more sensitive, or your analog sticks to be more sensitive, or your whole keyboard to have less travel time.
Having a hyper sensitive keyboard basically always results in a lower skill/dexterity player accidentally doing even more w/s or a/d nullification or unintended movements. This new tech is different.
It reduces the skill and dexterity required to play like a seasoned pro by intelligently changing the travel threshold dynamically depending on how far pressed the keys are and whether they are being released or being pressed down.
You say its like getting mad about mouse look in the 90s, and Valve, the people who revolutionized online multiplayer shooters in the 90s, is saying, no, its not, in fact, its so bullshit we are banning it.
FFS, the companies that are marketing these keyboards are themselves saying it either is cheating or is basically cheating in their marketing material and public statements.
And yes, while it has been technically possible for a long time to do weird things with inputs, most games and communities that take themselves seriously view certain forms of this as cheating.
Its getting banned now because now we have keyboard manufacturers just straight up releasing keyboards with features that exceed in speed what used to only be done by a handful of people with too much time on their hands.