Aggressively sculpted keycaps make a noticeable difference when you try to reach your finger to the further-away rows. Existing keycap profiles are actually *less* aggressive than they should be, especially on the number and F rows.
Try putting your hands on the keyboard with one of your fingers (e.g. the index finger) in as relaxed, neutral a position you can. Your finger should have a bit of a curve in every joint, especially at the second knuckle. Now, uncurl your finger a little bit. Ideally, your fingertip should now be right at the top of the next further away key. This is approximately what happens on a mechanical typewriter, because the keys are in a stairstep arrangement:
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Unfortunately, the bottom (ZXCV) row on a typewriter is really hard to reach, because when you curl your finger *more* than its relaxed position, it doesn’t really get any longer, but mostly just comes straight back toward the body. So on a mechanical typewriter, the top two letter rows and to some extent the number row are pretty easy to reach, but the bottom row is a pain in the butt, especially for the middle finger, which is a bit longer than the other fingers. This is why uncommon letters were placed on the bottom row of the Dvorak keyboard layout, which was designed for mechanical typewriters.
The earliest electronic typewriters and computer keyboards had completely flat/uniform keys. Some of them had a slight tilt to the key tops, trying to mimic the typewriter style, but regardless, they didn’t get nearly as much step as on a typewriter. Something like this:
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In the early 1970s, typists and researchers/keyboard makers at IBM and Honeywell figured out that you could make typing easier by using sculptured key tops. Look at the IBM Selectric II typewriters and beam spring keyboards, and certain Honeywell hall effect keyboards from that era. They have key tops with a shape roughly like this (but a bit taller):
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This shape is still the gold standard among keycaps available today. Look how aggressive the step is from one row to another. This shape is still not perfect in my opinion (it has less step between the home row and the further away rows than the typewriter has), but it’s better than anything else available (unless you DIY your keycaps or use a non-flat plate to hold the switches).
In the 1980s, the German government insisted that all keyboards be less than 3 centimeters tall, from the desk to the top of the home row keys, and insisted on a keyboard slope of less than 15°. I haven’t read the studies that led to this standard (if anyone can read German and knows where to find a copy, and wants to translate them, I’d love to see), but in my opinion this was a terrible set of conclusions to make from a human ergonomics perspective. But anyway, as a result, keycaps had to be shrunk down, and in general the step between rows was made less aggressive. Examples include “Cherry” profile and “Alps” profile:
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Later on, people who didn’t understand the point of the keycap shape designed even more watered down profiles, such as “OEM”, which is IMO inferior to the ones above:
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Among available keycaps, I’m also a fan of the shape of the keycaps on the Apple Extended Keyboard:
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In my opinion, entirely flat/uniform keycap profiles such as DSA, or SA when used on a flat keyboard with straight-stemmed switches, are inferior to all of the above:
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Look how wimpy the step is between rows.
For more analysis, see
https://geekhack.org/index.php?topic=68550 and
https://geekhack.org/index.php?topic=62444
