Actually, Locomotion No.1 with the benefit of hindsight, was a 'looking backward' design.
Single flue boiler, low efficiency cylinders sunk into the said boiler (to avoid condensation), driving position on the side to allow direct control of valves if required, (and thus to control speed/reverse/stop) - since the locomotive had no brakes!
The four locomotives of that class were very unreliable - it was the Hackworth engines that kept the railway running - despite (again with hindsight) their limitations.
Timothy Hackworth had worked with and for the Stephensons when Active No.1 (the original name) was built in the newly established works in Newcastle.
The pace of change was enormous. Rocket (just four years later) was the prototype of (almost) all later steam locomotives.
Actually, in terms of longevity, 1275 (long boiler 0-6-0) - to service 1874 and still existing might be a better bet!
(EDIT - should have also said that Rocket was obsolete within six months of the L&M opening.)