with the ubiquitous 2.2 gamma standard, the ratio between the brightest white and the darkest grey as represented in a game should be about 200000:1.

The standard for computer monitors is sRGB, which is very similar to gamma-2.2 overall, but extremely different when you look closely at the dark end of the curve. The darkest grey in sRGB is only ~0.0003 or ~3300:1 compared to white.

Some other standards of note are Rec.709 (Televisions), Rec.2020 (4K TV also brought in a new colour standard) and Rec.2100 (The fancy new "HDR" TV's...). Most console games will be authored with Rec.709 in mind rather than sRGB as the output colour space :o
One thing to note is that human perception of colour depends on how bright the background is... so sRGB displays assume that you're in a typical office lighting environment, while most of the TV displays assume that you're in a darkened room.

A lot of cheap monitors are actually only 6-bit, not 8-bit, and they use dithering tricks and adaptive backlights to achieve the same visual quality as a real 8-bit display, which means their contrast ratios would actually be less than what's theoretically required to display an 8-bit signal. Note that even mid-range monitors these days boast contrast ratios well over a million to one -- not a thousand to one.

Not sure about your numbers/units but I think you're right in the broad strokes. This is why "HDR displays" are the big buzzword at the moment.

sRGB displays (current computer monitors) are supposed to have a brightness of 80 nits (equivalent to 80 candles per square meter)... New HDR displays have a brightness of 1000 nits (1000 candles per square meter!), which when paired with 12-bit signals instead of 8-bit and new "gamma" curves, allows for much more realistic contrast.

Lux is a measure of how much light is arriving on a surface though, and nits (or cd/m2) is a measure of how much light is being emitted by a surface per angle. They're not directly comparable units :(
Also with your perfect albedo surface, it takes the 100K lux that's landing on it and re-emits it over the entire hemisphere, which divides that energy by Pi. A perfect mirror would not divide the energy by Pi, but would also not have any visible reflection of the sun from most viewing angles.

Million to one with dynamic contrast, right?
I haven't ever really paid much attention to that part. Have I been using it without realizing all this time?

Yeah they'll quote insane numbers like a hundred million to one "smart contrast ratio" or some such, meaning it's not really the true contrast ratio... Which means they can't show the darkest grey and pure white at the same time. But they can display them both perfectly at different times, but dimming the backlight in dark scenes and brightening the backlight in bright scenes. Most LCD's do this stuff automatically.