How much current a power supply is capable of delivering is only part of the equation (Ohm's Law) - the other half is how much current the load wants to draw, determined by its resistance (DC) and impedance (AC).
In short, you are correct that in this situation it doesn't matter whether you touch a downstream mains circuit protected by a 20A CB and lighter wiring, or a 400A main feed with a hulking big CB and half-inch-thick bus bars; both are capable of delivering enough current to kill any animal.
When you touch the Live of an AC-mains, a circuit may form between that point and Neutral (if your other hand happens to be in contact with that, for example), or that point and Earth, the danger is largely the same, because it only takes tens of mA current to put the heart into fibrillation (as distinct from actually cooking someone with several amps running through them).
Another factor of how deadly coming into contact with any high voltage source (with enough current capability to put the heart into fibrillation) is what that path is through your body. Electricians are taught to, where ever possible when in a high risk situation of contact with said high voltages, to try to do so with only 1 hand active, the other in their pocket. Because they're also trained to wear rubber-soled shoes/boots when on the job. The result is that there's much less likely to be a path for current to flow from the point of contact (finger) along the arm, down or across the chest (heart) to where ever the current could otherwise go (to the other hand, down through their feet). So your body isn't necessarily a path to ground, depending on the details.
Strictly speaking, your capacitance to ground and/or surroundings is there too, but in most circumstances it's a far less significant contributor to current flow (birds land on power lines all the time, even ones at thousands of volts, and are completely unperturbed, because their capacitance to anything/everything else around them via air is utterly negligible). (BTW your phrasing of the AC issues in your question suggests you think capacitance is some inherent property of a body (human, metalic, or whatever) - it's not, it's simply the surface area of an object in close proximity to some other body/lump-of-metal/etc - whether that's the track on the PCB to the ground-plane underneath, or the area of your feet to the ground beneath them, with some insulator (your shoes, pre-preg on the PCB, etc) between them.
The thing with skin resistance is that it varies dramatically, for the individual, on their level of hydration & sweating, and also on how much surface area of their skin comes into contact with the Live conductor. Here, measurements of/by one individual aren't really helpful. And even a few tens of mA, if it crosses the heart, can be enough.
So it's a combination of factors that determines how severe an electric shock from 50/60Hz mains is.
Another aspect of these scenarios is moderate and high voltage DC (> 50 Volts DC), which can be much more dangerous. With 50/60Hz mains, that reversal of voltage results in a reversal of the current, 50/60 times per second, which can be an opportunity for a human to pull away from it (and for a switch to open). When it's DC, and you touch it, your muscles are much more likely to 'lock on', and even grab the high-V conductor even more which increases skin contact surface area, and you stay connected, and if the current path is through the heart, say goodbye.