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Another benefit of a flat torque curve is that shifting becomes a no brainer. It is easier to drive th ecar around town as it's making decent HP at lower rpm. Then, when letting 'er run, you don't have to be as precise about shifting at the torque peak. That's not to say you can get max performance by shifting at any 'ol rpm, but overall driving experience is better.
Remember that 300lbs-ft is what the driver can feel. That is the force that causes the car to move. HP is a measure of how long it can do it. That's why super peaky high rpm engines can accelerate cars so well. Remember the fictional car that makes 300lbs-ft at 1500rpm and at 4000rpm. It matters not what rpm you are at, you have the same force available to you.
This is where gearing becomes important. People stopped thinking about gearing when automatic became the number one choice, but it's not so simple. Making torque at high rpm is usefull because you can use gearing.
This summer in the Yukon we had a tour of a sternwheeler paddleboat from the goldrush era. A neat machine that took HUGE advantage of gearing. It took THOUSANDS of foot-lbs to twist that giant wheel through the water. How did they do it? A giant engine? Sort of. The thing didn't make tons of torque (as literally required) but used torque multiplication through gearing.
Suppose we go back to our 300 ft-lb MB engine. Could it run that boat? You bet! The boat ran the wheel at only 22 rpm. Take you engine that makes 300 lb-ft at 4000rpm and gear it down to 22 rpm. Thanks to the wonders of gearing, we can exert over 54,000 ft-lbs on that paddle-wheel. Of course, in cars we want speed and gearing that has the engine spinning at 4000rpm and the final drive at only 12 rpm wouldn't work too well. The lesson is that we can always use rpm and harness it with gearing.
That is how cruise ships use engines that are small (huge, but not considering the boat size) to run props that are so enormous it's insane.
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