This rumour suggesting that Switch has 1080p screen and much powerful version, so I very doubt about whole rumour.

The rumor also says that the dev kit is more powerful than the PS4 Pro, made for 4K gaming, in a handheld device.
I know the dev kits are usually more powerful and more expensive than the actual console, but it just seems completely exaggerated.

Well, it is "Foxconn worker rumor" number 3 or 4 now, and the previous ones were debunked, so...

Not a lot to go on. 

X2 is based on the parker tegra SOC. has a GPU with the same 256 cuda cores X1 uses but both the CPU and GPU is ran at a higher clock. Benefits of being in a 16nm fab process as opposed to a 28nm process. 

No mention of memory bandwidth but X1 had around 25GB/s on a 64bit bus. The Pascal based X2 should have double that since it's supposed to use a 128bit bus so we are looking at around 50GB/s memory bandwidth. It's also most likely using LPDDR4 just like the X1 so the gains in memory bandwidth come from the league bus width. 

X1 used a 4x4 CPU core config. Low power and high power CPUs. Parker (X2) is supposed to be using better all round CPU cores but in a 2x4 config. No idea it that will carry over to the Switch. 

I am surprised they are going with only 4GB of ram though, being that the Parker specification has support for up to 16GB of ram. 

The battery life is going to be low when gaming. The thing is 1/2 the power of the Xbox One, there is no miracle tech coming to provide it with 10hours battery life.

Tag.

I did say rumor, take it with a grain of salt. The 4K bit is a load of tosh.

On par with Xbox One then?

Not at all. Its got some nice tricks up its sleeve and it comes close in some arbitrary areas and may even be better in others. but over all, it's about 40-50% as powerful as an XB1. That's pretty decent though for a handheld device. 

5200 MaH for the battery (w/Joycon batteries factored in) is pretty small.

The Google Pixel C battery with a Tegra X1 is 9200+ MaH, and granted that has a larger screen, but it also only runs the X1 at 80% peak clock (meaning its down-clocked significantly).

I'd be surprised if 5200 MaH gives you even 3 hours unless the Tegra chip Nintendo is using is massively downclocked in portable mode (which isn't a good thing).

Apparantly 256 CUDA cores at 921 Mhz yields about 471 GFLOPS 32bit FP.