In real life, traction control used to be the "cheap" alternative to proper ESC. Which honestly I feel often was more for marketing than real benefit because the cars that only got TC rarely had engines with so much torque or power that you needed TC in the first place. For example my previous car was a Ford Focus MK 1 with the 1.6 litre gasoline engine which got 100 HP and 145 NM of torque. It simple has no use for traction control because this car will never have any significant wheel slip unless you literally force it into it. (As in reving the engine like mad and then releasing the clutch violently.) There is no significant risk of accidental overtorque because there simple isnt enough of it when you dont drive like a total idiot. The sensors reqired for ESC simple mean that TC is just an addition in software.... there is no reason not to have it because the hardware is already there anyway.
The current implementation does lump the 2 together in the LUA and in the user interface. The control keybindings list ESC/TC mode, maybe there'll be changes in the future. Some of the IRL contemporaries to vanilla vehicles were available with TCS without ESC so the feature would be realistic. Your take is not particularly accurate in the actual history of traction control implementation. The usefulness of TC is really on a case by case basis. For starters, the general intention of TC is to regulate the slip of driven wheels relative to the actual vehicle speed. This applies in corners too. In the context of modern ABS wheel speed sensor based TC from the late 80's, the high end Mercedes-Benzes, BMWs, and Toyotas fitted with such systems were reasonably powerful and RWD. Their engine control methods tackle the over-speeding of the driven rear wheels relative to the fronts. This helps prevent unintended power-oversteer in corners and may also help to preserve stability in certain cases when the road surface conditions are inconsistent. Note that the Benz and Toyota TC had combined engine control and wheel braking, will expand on it later. Engine-only TC is certainly less useful in FWDs, but it helps in reducing driven tire wear with drivers who can't properly control, say, a Mazda 626 with the 2.5 V6. The only 626 variant that could be optioned with it was the most powerful one... Benz introduced complete TC nearly a decade before ESP. TC wasn't a cheap alternative back then, there was only it and ABS. Using 4 channel ABS as a base, a complete TC only requires the addition of some relatively simple programming to the ABS controller and a link and control to the computerised management of the engine (though some Toyotas use an additional engine throttle device). Not a big cost issue as vehicle computerisation was a growing trend throughout the 80's and 90's. Or one could cheap out like Ford initially. (See bottom) Approach it the other way as a profit driven business in the context of an economy car, it's not that TC is a cheap alternative, it's that ESP is a pricey add-on. ESP requires additional sensors, let alone the complex calibration compared to TC. Though no doubt ESP has a greater effect on safety as it can react in situations unrelated to the propulsion of the car, business is not always the most ethical thing. Profit margins, noteworthy incidents, cost-benefit ratios, and safety legislation are factors in deciding on ESP implementation. The Mitsubishi Mirage in my region only has ABS. Also, ESP regulates yaw, not wheel spin of drive wheels. The systems from TC's engine control portion still play a part as the source of the vehicle instability could be engine power. The yaw correcting individual wheel braking of ESP would not be effective if unregulated power was still being applied. Back on wheel braking and TC, I'll use the Porsche abbreviation of ABD, Automatic Braking Differential to refer to braking in the TC context. The ABD function brakes a driven wheel when it's spinning excessively faster than the other wheel on the axle. (Assuming there's no need to explain open/Limited Slip/Torque Biasing/locking differentials here) ABD is useful when driving off in poor conditions when the surfaces beneath each driven wheel are non-level and/or have varying friction coeff. This can happen regardless of power and the driven axle(s). There is some merit to the usefulness of ABD, while TC's engine control can usually be mostly disabled, many cars sold in First world economies today feature non-defeatable ABD systems at sub 80 kph speeds. Especially if it's developed in the EU and/or has AWD. As mentioned earlier, ESP controls yaw on the move. The ABD function of TC allows a vehicle with open diff(s) to start moving in the first place. Fun trivia: Porsche and Land/Range Rover are notable early adopters of such partial TC involving ABD without engine control, though eventually both would add the latter, Porsche did it when switching the 911 to water-cooling. Porsche was also among, if not the first to combine ABD functions with mechanical rear LSDs in mainstream road vehicles via the 6-speed 993 C4. Fun trivia 2: Ford/Mercury/Lincoln had their own take on TC without engine control in certain large cars with the Modular V8, it was bundled with ABS and utilised single and double wheel braking across the driven rear axle. The only thing to say is that they added engine control later to better compete with GM's complete TC system.
The problem is, as of 0.18.4, the traction control compared diagonal opposed wheel, which is incorrect and will fail a diagonal ramp AWD test
This is not correct. The logic deployed is not wrong in any way and is used exactly like that in real life as well. Diagonal AWD test is not something a car has to master, in fact, it's not the common case that a car can do it. Heck some awd cars even fail with a single roller IRL.
