Actually battery life of gaming laptops is really good, because it’s made to hold a discrete GPU which can usually be turned off, I used to get around 6h of battery for day-to-day stuff in my gaming laptop when I recently bought it, I haven’t used it outside of a plug for a while so I assume the battery would be in a bad state today.
I get the point of having to upgrade the whole system every few years, and that they’re more expensive, but if you need portability a desktop is not viable, e.g. I moved countries a few years ago and I’ll move again in a short while, a desktop is just not practical for me. Plus I’ve had my laptop for 4 years, which is much longer than my deck.
So if I want to play games that I have issues with playing on my deck, like Doom or Cities Skylines I play them on the laptop. Granted, I could plug a keyboard and mouse to my deck, but like I mentioned I already had the laptop for years when the deck came out.