Steam Deck have Steam library (and any PC store as well). It's better than any console in terms of software 

PSP outsold 3DS.

Until now, not be true.

Steam deck compatibility

Great machine, much lighter than I thought, and powerful, but have some problems (battery life and heavy users may suffer a little).

 A great secondary portable console. 

It's easy to come out with your own version of something that already exists and make it better. So the Deck is better than the Switch on a technical level, big deal. The Switch paved the way for all these wannabes, so it's still number 1 in my eyes.

If anything, the Deck should feel embarrassed that a five-year-old, technically inferior system is still kicking its butt.

Comparing the Steam Deck to a Switch is actually fairly silly. They target two very different markets.

Also saying that there's something wrong with it because there's a compatibility list is pointless. The Steam library is huge and most of the games need keyboard and mouse. Just stick to the subset of games that are designed to run on the the device...

Maybe one day Valve will "properly" enter the console sector, of course... The Steam Deck may just be the starting point.

And the software support on Steam Deck is great. Already over 5000 Steam games have a positive compatibility result:

https://steamdb.info/instantsearch/?refinementList%5BappType%5D%5B0%5D=Game&refinementList%5Boslist%5D%5B0%5D=Steam%20Deck%20Verified&refinementList%5Boslist%5D%5B1%5D=Steam%20Deck%20Playable

Over 4000 of them with a SteamDB-rating of 70+, over 3400 of them with a SteamDB-rating of 75+, over 2700 of them with a SteamDB-rating of 80+, over 1700 of them with a SteamDB-rating of 85+ and over 700 of them with a SteamDB-rating of 90+... so wherever you draw your personal "quality line", there are lots and lots of good games to play: 

Plus thousands of PC games not yet rated by Valve, but already running great on Steam Deck.

Plus thousands of console games already running fine via emulation... from Atari 2600 to PS3 / Xbox 360 / Switch games.

Plus streaming more demanding console and PC games if a good internet connection is available: Steam Link, Stadia, Xbox Cloud, PS Now...

Are you stuck in the 2000s? Over 16000 Steam games have full controller support.

And even many older games without controller support play great on Steam deck due to official or community control templates (keyboard commands are assigned to buttons, mouse movements or keyboard commands are bound to the sticks).

ADDITIONALLY you also have the trackpads and the touchscreen for mouse movements.

Even if the Steam Deck is heavier than a Switch... the weight distribution and ergonomics are great; the Steam Deck is very comfortable to hold.

The grips of the Steam Deck (that's where the hands go) stay cool, so the heat ain't a problem:

Battery life totally depends on the games and game settings. Many PC versions on Steam Deck have a better battery life than the Switch version of the same games on my 2017 Switch... with better settings on Steam Deck.

My point is - just play the games that play well on a handheld.  Better yet, play the ones designed specifically for the Steam Deck.

It's a handheld PC. It's a niche product appealing to a rather small audience that's different from the audience the Switch attracts.
It was never going to rival the Switch in sales. Anyone who actually believes this nonsense that it could do so is delusional.

In terms of power it's obviously way stronger. But the short batterylife to me personally is a deal breaker. Might not have been one if I really wanted a Steam Deck, but I was only slightly interested anyway.