There are exceptions to the rule, and it sounds like your brother's Freightliner is one, or the toe-in was just way too extreme.
Back in the day more toe-in was used because the suspensions were loose enough that the front tires straightened out at speed. When you slowed down for a turn the wheels returned back to toed-in and understeered to make it more controllable. Today's rack-and-pinion MacPherson front suspensions require less toe-in.
If loading or unloading the suspension are causing toe changes, you have a problem in your Ackerman angle or your tie rod angle. Simplistically, draw a line from your kingpin to the center of your rear end. That line should intersect the outer tie rod joint (if the tie rod is in front of the axle, measure where it would be if flipped behind the axle). If your Ackerman is off, you will get dartiness and bumpsteer. Your tie rod should also be parallel to the control arm. If it's significantly off-parallel it can cause the same problems.
[storytime]
My team's first race car was a lowered MR2. Our team captain was trying to improve the handling and read how lowering the car would cause bumpsteer, so he ordered a tie rod flip kit. Instead of mounting the tie rod end to the bottom of the spindle, the kit moved the mount to the top to keep it parallel. For some reason, the kit he bought made it worse. At the start of test-n-tune day we had a semi-pro driver in the car, and he hit a bump on the front straight at Eagle's Canyon. The car bumpsteered a full foot to one side, and he immediately slowed until he could get it in the pits. We jacked the car and everything looked good, but a friend on another team noticed massive tow change as we were jacking it (cue Beavis and Butthead laugh). The tie rod flip was causing the massive toe change and bumpsteer.
The flip kit required drilling the tie rod end taper into the top of the spindle and installing a bushing to neck it back down to the right size, so there was no way to un-modify the spindles. Fortunately we had a spare set of stock spindles, but they still had the brake backing plate. I asked my team captain about removing the plates and he said we'd need a press to split the bearing off the spindle so we could get them off. I installed them as is. We ran the rest of test-n-tune and the car steered great, problem solved.
The next morning I started in the car and did a full stint with no issues. The team captain got in the car and drove for about an hour, then called in. "I think the brakes are going out."
I answered "Bring it in and I'll check them."
"Never mind, I think they're fine... OH CRAP I HAVE NO BRAKES!"
I started getting tools lined up and after a minute heard him coming into the paddock spot.
The brakes were on fire with blue-green flame coming out of the wheel, and our fire extinguisher was up on the hot pits. That friend from another team? I stole his fire extinguisher. It's a b!+ch trying to put out a brake fluid fire on a lowered car. Fortunately we'd cut out some of the inner fender, and I was able to pop the frunk (MR2, engine in back) and extinguish the fire from the back side.
The brake shields had trapped heat in the rotors and we ate through a brand new set of race pads in about three hours of track time. You couldn't hear the brakes grinding, so it also ate through the backing plate, and about 1/4" of the piston itself, until it came loose enough to lose the brake fluid. The flashpoint of brake fluid is over 900°, and the rotors were there.
My team captain was stressing over how we were going to remove the shields without a press, and in the meantime I grabbed a hammer, a chisel, and some channel locks. In about thirty seconds they were gone. We threw on another pair of used calipers and a set of O'Reillys cheapest brake pads and ran the entire rest of the race with no issues.