Wrong. The war IS potentially winnable by conventional means but it is beyond the means of what the galaxy can currently do.
Keyword there is currently. You are thinking too much in the box.
Consider that the war would last centuries until completion of the harvest, ie: Exterminating every single being on every single world. The Geth dont sleep. They don't eat. They can live anywhere including in the cold darkness of space. Their workforce churned out a dreadnought in MONTHS.
Now imagine what they could do if they had half a century. A force capable of challenging, and maybe even defeating the Reapers could be constructed by the Geth EASILY.
Good thing you aren't in charge of war strategy. But then again, that's probably why you Quarians lost your homeworld and all other colonies to a bunch of machines.
No, good thing you are not in charge.
Could the Geth construct a fleet capable of going up against the Reapers given time and resources? Sure they could.
Would the Reapers allow it to happen? No way. They'd attack the shipyards, they'd attack the supply lines, they'd infiltrate everything with indoctrinated people or hacked Geth.
To withstand the Reapers long enough to build their fleet the Geth need a huge fleet as defense force. Where exactly would they get that? Do you think all other species would give up their last defenses to help the Geth? Earth, Palaven and Thessia are burning, billions are dead and converted into husks. Should the galaxy give up everything on the off chance that the Geth can match the Reapers in terms of building a military force? Cause that's not going to happen.
The Reapers were the weakest right at the start of the war. Since then they turned millions of people into ground troops, wiped out the fleets of entire star systems and are indoctrinating everyone in range. How exactly would the Geth defeat the Reapers if their army grows more slowly? Maybe their strength was 1000:1 at first but the longer they wait, the more skewed it becomes. By the time the Geth are finally ready (assuming the Reapers allow them to continue), it would be more like 50000:1.
Also, have you done the math? Each capital Reaper needs to be countered with several dreadnaughts. Let's say 5 for each. The Reapers have at least 20.000 of those, which means you'd have to build 100.000 dreadnaughts. That's not counting the smaller Reapers or the ground forces.
If the Geth need 3 months to build a dreadnaught, then they'd need 25.000 years to build their fleet. 
Oh sure, ideally you'd build nothing but fabrication units that replicate, then switch production to shipyards and the vessels themselves... but the Geth aren't using nano tech or anything like it, so it would still take thousands of years. Btw... the Reapers have nano tech and can convert a person into a foot soldier within hours. 
Edit: That's just time. If you take the resources into account, it becomes even more ridiculous. Do you have any idea how much Element Zero you'd need to build all those drive cores? What about rare metals and alloys for the hulls? Where is all that supposed to come from? Mining and processing takes time, too. You'd have to strip mine millions of asteroids to get those resources, I doubt that's possible without Reaper interference.
Modifié par DaemionMoadrin, 22 juillet 2015 - 08:38 .