If you re-arrange the keyboard into a shape according to human hand ergonomics, you can easily fit a number row that is easy to reach without making typos. See kinesis advantage. It's hard to imagine how requiring me to press two different keys for the same effect would increase speed and reduce typos. I suspect the effect is completely opposite. (Shift is painful enough and I hate typing camelcase code)
Number keys are also indispensable for games where you need to switch items while moving. A finger or two are already going to be busy with the motion keys, adding two more fingers that don't overlap with the motions is going for some octopus keyhandling.
The further keys on a sculpted Kinesis keyboard are angled the wrong way for comfortable typing (this is an unfortunate artifact of their curved PCB technology combined with lack of first-principles analysis by the designers). You want the switch axis to remain perpendicular to the hand, because flexing the proximal joint of the finger is the way people press keys, and using the whole hand to stab at further keys the way the sculpted Kinesis board requires is not particularly comfortable or efficient. There are also several other design problems with the Kinesis boards, but this isn’t really the right place to discuss it at length.
It’s certainly possible to have 2 rows of reasonably reachable keys past the home row (especially if the tops of the further keys are aggressively raised – think 1950s typewriter). Even in the best case those keys are substantially slower and more error prone (and less comfortable) than the home row or next row above, but with decent design can be made nominally acceptable to type on.
But it also works a bit better in practice to put more functions (like numbers and common symbols) on shifted layers, as long as the shift keys are conveniently located. Using pinkies for shift is not the most comfortable choice, especially pinky keys which are a stretch to reach. Modern keyboard layouts are quite terrible for making common computer code symbols accessible.
If you find it uncomfortable to hold down a shift key, consider trying a sequence of key presses instead. That is, let your "shift" just act as a dead key, modifying the immediately following keypress. Try putting your various shift keys on a thumb or forefinger. https://en.wikipedia.org/wiki/Dead_key
I have no particular insight into game inputs, except to note here that a significant proportion of serious computer game players develop severe RSI because their use of keyboard hardware is extreme (and arguably the hardware they use is not very well suited to handling the job safely).
I use a Kinesis Advantage, and although the number row is indeed easy to reach, I still prefer using an embedded numpad on a layer. It's just faster, more accurate and feels less awkward than the number row. Even on the Advantage, the numbers 1, 5, 6 and 0 are awkward to type when using the number row.
EDIT: I agree with you about the gaming aspect, though.
Number keys are also indispensable for games where you need to switch items while moving. A finger or two are already going to be busy with the motion keys, adding two more fingers that don't overlap with the motions is going for some octopus keyhandling.