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Horsepower is an expression of torque and means something when talking about a car's absolute ability to accelerate.
You analogy is right. Torque is how much work the engine can do. It's how much it can lift. The horsepower is how much it can lift, how fast.
Gearing plays a strong role. The higher you can have the engine rpm the more room you have for gear reduction. Gear reduction is a torque multiplier. Suppose we have that mythical Mb that makes 300lb-ft at 4000rpm. If we have such an unbelievably steep gear that the wheels are only turning 10rpm while the engine is spinning 4000, we have:
4000rpm/10rpm = 400 multiplication factor.
Take your 300 lbs-ft and multiply it by 400. That's 120,000 lbs-feet of force available. That's an amazing amount of force!! You are going very slow, but you couls push a huge vehicle along. This is the principle that boats and huge tractors (semi's) use. Super steep gears that allow enormous torque multiplication.
But, from the math, can you see why it's so important for an engine to make rpm? AND make that torque at high rpm? It allows greater gearing flexibility and torque multiplication.
Take our above example. Suppose that we operate that engine at 1500rpm.
1500rpm/10rpm = 150 multiplication factor.
Now we have only 45,000lbs-ft of torque available. We want the engine to be spinning fast and the final drive to be spinning slow if we're going to have huge force amounts available.
Why do you think that little Honda S2000 can rip off sub 6.0 sec 0-60 runs with only 240hp and a super peaky torque curve? RPM baby. Motocycles take advantage of the same thing that big trucks do. RPM and gearing. It is always prefereable to have an engine that makes high torque at high rpm and use gearing than an engine that makes high torque at low rpm. Of course, many engineers have spent tons of time trying to figure out how to have both. Variable intake runners, variable valve timing, variable exhaust baffling, etc.
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