I'm like 97% sure you don't just buy a GPU or CPU by itself to mine. You need power supplies, motherboards, fans, etc. And 300w is not the power usage, it's the TDP. And you're forgetting that the network gets bigger over time so you get diminishing returns. It's simply not worth it.
You are absolutely correct.
Without a motherboard, (ram) and a power supply a gpu and cpu won't work ... I can't believe I have to say this lol.
You can technically get away with not having fans if you build a passively cooled computer. (Obviously not a computer with a Threadripper)
The TDP is close enough to power usage for this scenario.
For example if you go to pcpartpicker and add a Threadripper 3990x as the cpu it shows the TDP as 280 watts.
If you click out of that and go to the main page it shows Estimated Wattage: 280 watts.
I used 300 watts as a conservative guess ... almost a bit too conservative.
Without a video card the wattage comes out to about 389 watts.
https://pcpartpicker.com/list/NB7H7T
Compared to the cost of the $4000 CPU the price for the motherboard, fans and power supply are insignificant, roughly 10% of the price.
This of course changes if you add multiple $1000 graphics cards, but I was only curious in this new CPU's performance.
As I mentioned at the bottom a 3950x would be better CPU to mine with.
Not only is the 3950x cheaper the AM4 motherboard (also cheaper) they are in would be able to use more graphics card in total than a Threadripper's motherboard.
The Threadripper motherboard above supports 4 graphics cards
Compared to the 12 graphics cards you could use in a conservative 4 computers with 3 graphics each all using a 3950x
As for "the network gets bigger over time so you get diminishing returns" that's the whole point of cryptocurrency.
If the network remains small then nobody uses it.
If the network remains small then a 51% attack is more likely
As the network grows and becomes more popular the value of the coin rises to meet demand.
Most cryptocoins do have a difficulty setting that increases with time and the total amount of mining activity (hashes per second) of the network.
Without a "difficult setting" most coins would mine and absurd number of coins as more efficient CPU and GPU are released and or coins with finite supplies like bitcoin would quickly mine all their coins.
Bitcoin has another method that retricts the production of bitcoin
When a bitcoin block is solved the person and or mining group is rewarded with a set amount of bitcoin for performing the calculation.
The reward is a set number that decreases over time until only 21 million bitcoins have been mined.
The decrease happens about every 4 years and is called a halvening which does exactly like it says and cuts the reward in half.