Actually try the build before forming an opinion about it. It was surprisingly effective. It had ERPPC's before the heat nerf removed them from the game. Weapons are meant to be fired all at once, holding shift (default) to keep armlock on. Since they removed 6PPC boats, 40 is as good as pinpoint damage seems to get.
We already know this mix of weaponry, since Gauss and Dual AC20 were nerfed this is not a uncommon build of weapons on several mechs. Yeah, they are effective for pinpoint damage and on a Atlas it's a killer as he will last for two or more cycles. I am not a fan of chasing lights with a AC20 however, which is where your achilles heel is with the 90 meter min range on the PPC's. As for your remark about 6 PPC boats, I can only say good riddance as they spoiled the gameplay.
No, why should I? I don't need to in order to give you feedback on weapon applications and limitations. I have used PPC's and AC20 in conjunction before on Atlas and that I know something about... In order to rate this build, yes, it's a good idea to try the exact build. Which is why I did not rate it. I know you said to try before forming a opinion but if we did that for every build this would be one empty forum. Theoretical texts will always be posted, ratings however we try to give fairly after trying.
Used to run this at one point. I would actually think the higher armor of my version would help alot when it comes to protecting your arms from falling off. It is probably worth the loss of a DHS (or two) That, and I have AMS, a must for atlas, for both itself and as an AMS umbrella.