I dunno what laptop you use, but my iPad Pro + keyboard is materially smaller and lighter than my full-sized 15" laptop.
"plus you probably need a stand and mouse as well to reach the physical usability of a laptop"
Apple was first, but there are now SEVERAL keyboard cases that function more or less like Apple's fancy & expensive "Magic Keyboard." Like Apple's, they usually include a touchpad.
My iPad Pro in my Magic Keyboard folio is not much bigger than the iPad itself, but opens up into a very very usable and stable configuration. The hinge holds the iPad above the keyboard, so it's at a more comfortable heigh. I can easily use it on my lap, for example, which is typically a use case that tablet-keyboard combinations fail at.
(The only downside of this style of keyboard case is that you can't fold it all the way around; to work with the iPad in portrait mode, you take it off the keyboard -- which is also simple, since it's just magnets.)
IOW, the "physical usability of the laptop" threshold is absolutely reachable with a single accessory.
Also, even though I have a fancy iPad and fancy keyboard case, my iPad solution is materially less expensive than my laptop, so taking it places represents less of a risk. And obviously it almost never needs to be plugged in. (This gap is narrowed for M1 hardware, but I'm still on Intel.)