If you're using a laptop on your lap you've already given away any chance of ergonomic comfort.

Yes this has always annoyed me; having it centred under the keyboard makes no sense except in some weird universe where everybody uses only their thumbs to operate the trackpad. Trackpad alignment was one of the major causes of my RSI due to the horrible bend in the wrist it causes.

I haven't used a Mac in years but the one thing they always nailed was the trackpad. It's big and actually centred on the laptop body.

I think it depends on how much you type. If you type most of the time, your hands will tend to stay centred on the keyboard. Of course this is highly variable based on so many factors...

Yes this is true, I see your point, with a laptop on your lap, in order to balance its weight optimally, you need to centre it relative to its mass, not relative to the hands rest position (F and J keys) so then when you have to type you need to move your hands sideways and it's not very ergonomic.