Synthetics aren't better than organics, they're different. They face a different set of challenges than organics, but the challenges and limitations are still there. The reason the Reapers decided to wipe out organics isn't because synthetics were better, it was to prevent what they thought were inevitable wars between synthetics and organics. There are two examples in the games that organics could defeat synthetics... the Quanri/Geth war (the Geth would have been wiped out without intervention from the Reapers) and the defeat of the Reapers at the end of ME3.
Of course, the Reapers didn't think they were wiping out organics, they thought they were preserving them. Well, preserving the life they thought worthy enough to preserve.
Let's test your theory about magically reviving machinery with energy. Take the power source out of your computer and let me wire it directly into the A/C power in the wall. Let's see how fast that A/C current fries your D/C regulated machinery. Or, let me take the battery out of your car and then require you to start it with a AA battery.
This is why most folks recognize the synthetic ending as Space Magic.
The war in it itself is not a problem, the problem is that combatants are unewen to such a degree that one side will inevitably lose, and subsequently put in danger not just itself, but all organic life. Synthetics dont need organics. They dont need food, clean water or plants. They dont need sunlight. A dyson sphere around the sun that puts the entire star system into total darkness wouldnt afect them negatively at all, but would kill off all organics, advanced and non advanced that exist in the system.
Again, Geth and Quarian conflict is miniscule on large scale of things. Say Reapers didnt get involved, and Quarians utterly destroy Geth. Can you say that in the following milion or bilion years someone somewhere wont create synthetics?
My point is timescale. It is inevitable that something will happen given enough time.
Its not just about preserving the curent advanced life in Reaper form. Its about preserving the "younger ones", the lesser evolved species that would be put in grave danger in case of synthetic victory. Simple as that.
Apples and oranges. My computer isnt a synthetic/robot, nor is that the case of energy drain. More suitable example is someone cutting electricity to my city/country for 10 years. A man who hasnt eaten for 10 years is dead for 10 years and no ammount of food showelling will revive him. I can plug in my computer after 10 years of inactivity and it will work just fine if preserved from damage.
Also sorry for bad writting, I was on mobile last time