Windows not recognizing onboard graphics!

Don't quote me on it, but I don't think Windows can switch graphics natively like you can on OS X. Whether there is any way round this with drivers I'm not sure.

Running Windows via Parallels won't help battery life at all, it probably defaults to the dedicated GPU and you're running a VM which will use more battery anyway as you're running two OS's.

 

On Macs with dGPUs, when you boot into Boot Camp, the EFI will disable the iGPU. There is no workaround for this.

So you can forget about Optimus.

The only way to get Optimus working is to setup an NVIDIA eGPU on an Iris-only MacBook.

 

Windows can and supports even multiple ways of handling multiple GPUs. It can keep independent GPU drivers running but Optimus is usually the best way. It is just a graphics driver that sits in front of the real graphic drivers so the operating system has only to deal with one driver and in the background it can seemlessly switch GPUs any which way.
OSX switching is worse because the two drivers support different things. There is no seemless switching unless a program has two code paths for each built in and can handle the context switch. Usually when higher gpu functions are called a framework is loaded for the active GPU or always the dGPU and you cannot switch back until it is unloaded again.

For unkown reasons Apple disables the iGPU entirely on its notebooks for Windows. If the GPU was visible a optimus driver would work even without official Apple support. But they prohibit it still for some reason. People tried to look for workarounds but there was none ever found.

Parallels will run on the IGP if you force the Intel GPU with gfxCardStatus(a little free tool) before launch of Parallels.