Your point about a minimalist UI is a valid one. Your post, however, was stupid. A picture of the base UI is not meaningful. There is nothing meaningful about base UI. It's a steaming pile of kludge. Minimalist is not the same thing as "no addons".
And as an aside, if your computer is overheating trying to run a few addons in WoW, you have much more serious problems.
I can relate to the "less custom UI is bettter" argument, mainly due to how terrible my computer is. Being a raidier, my computer stresses more and more every time something new comes out. In order to combat some issues of both computer side lag and overheating my computer, which cause more computer side lag, I try to run only the bare minimum. In my mind, the bare minimum is Recount, Omen3, Grid, and DBM or Big Wigs.
In this screenshot I have DMB, but I have converted to Big Wigs because I find it more accurate and dependable.
As you can see, their is a lot of room for vision and mobility. Their are a couple of downsides however, the biggest one being how you have to track both h4b and SnD on the default buff bar on the top right. Call me old fashioned, but I find this to be easier than messing with cooldown timers and bars. Another thing to be taken into account is how blizzard has implemented a lot of useful raiding tools into the default ui, even since BC
Is this to say that this UI is the one for you? No. But if your computer tends to have trouble, even just for raids, and you want to ease the pain while increasing visibility and raid awareness, this may be for you. This idea is taking your UI back to the basics, and it works well for me.