I don't think people realize how powerful this supposed device would be. 12SMs and dlss would put it literally close to a series S from a GPU perspective; possibly even above depending on how much they push the clocks in docked mode. While the leak is undeniably true info, I'm very much doubtful that this is what we will end up getting, specifically because it sounds like way too much.
Switch already has better battery life than the Deck. That can have as little as an ~1hr 20 minutes. Minimum on Switch is ~2 hours 30 minutes...and that's for the OG model. the Lite, Switch (2019), and OLED models have minimum of 3 hrs. Steam Deck also maxes out at about ~8 hours while Switch 2019/OLED can hit ~9 hrs.
the Switch doesn't play at the same graphics/performance as the Deck so the lower battery life isn't surprising. For what it is, the Deck is reasonable. Switch 2 is never going to have amazing graphics (such as a full PC game) so it can squeeze more battery life out. It's not quite fair to compare them both but yeah the Switch is the better portable/handheld device since you can actually use it for longer without having to plug in to a wall.
Probably the most likely scenario is that this is the 'GB Colour' of Switch. Big jump in graphical power, several games that run on it but not on previous models, but marketed as a revision and not a successor.