Ive got a 6 speed and have been changing gears the same way I would on any other bike.
Am I doing it wrong?
I'm not sure that's true. On my road bike, I mostly
only use the right hand shifter until there's a hill.
I'd not ridden my Brompton for a while since the first lockdown, but took it out to do the virtual Ride London event and had completely forgotten how to change gear. Kept just using the right hand shifter and making huge step changes.
It is one of those things that should work better. There's only six gears, so having two shifters seems unnecessary and it would be easier if you had sequential gears on one shifter, But I understand why it's done that way, and having a hub and a chain pusher might actually be better than a derailleur due to how low it all is.
But, as said above, you do just get used to it. (And quickly get unused to it too.)