I don't see how CPU mining would prevent mining industry from taking lion's share of all produced electricity from the whole world.
OK. Let's count.
At the moment, the Bitcoin network has a capacity of 100 EH/s. This number is 100,000,000,000,000,000,000 H/s. Antminer T9 has 11.5 TH/s = 11 500 000 000 000 H/s.
100,000,000,000,000,000,000,000 / 11,500,000,000,000 = 8,695,652 miners.
Each T9 miner consumes 1690 watts.
8 695 652 * 1690 = 14 695 652 173 W/h.
Now multiply by hours and days.
14 695 652 173 * 24 * 365 = 128 733 913 043 478 W/h/year.
But this is not an exact figure, because miners are different. The network still has a lot of old miners that consume much more electricity than the T9 or S9.
Now add to this number the mining of other cryptocurrencies. The farms on the graphics cards are so hot that some people use them as heating in the winter. Even if we just assume that this is the same consumption as the Bitcoin network, then we get that the total energy consumption that is used for mining = 128 733 913 043 478 W/h/year.
World output as of 2016 = 24,816,000,000,000,000 W/h/year. Transmission loss is about 20%. Thus, total consumption cannot be more than 20,000,000,000,000,000 W/h/year.
To division ...
20,000,000,000,000,000 / 128,733,913,043,478 = 155 parts.
100% / 155 = 0.65%
That is, now at least 0.65% of all the electricity that is consumed in the world goes only to mining. And this number is constantly growing. After 2 years, it will grow to 5%. After 10 years, up to 30%.
Now, if we completely turn off all the miners, and all the network maintenance work will be assigned to computers that are constantly working (because we already use them for other tasks), then all these energy costs can simply disappear.
Based on your image, pool miners look for different value range, which means parallelization is still possible and there's gain from joining mining pool.
If it's wrong, then the image illustration is wrong.
No, you just do not understand it correctly. Ok, when I have time, I will redraw this diagram more clearly + add numbers. Maybe then you will understand.