That's for newer AAA games. Games with simpler or more optimized graphics, especially those running in emulators, tend to do really really well.
I ended up buying one of those Anker laptop USB PD chargers, and they can recharge the Deck twice over, so I could actually spend nearly 8 hours fully utilizing the Deck's power without being tethered at all.
Just attaching any off-the-shelf USB-C powerbank is perfectly viable right now.
It's not like you do your 2 hour gaming sessions while moving around all the time. If you're sitting down, a thin wire to a decent size power bank isn't going to interrupt your gaming.