You always have to build your train according to the various weights of the cars making up your consist. Put simply, you can’t put a lightweight high center of gravity car like an empty hopper (MPC 9111 N&W for example) ahead of a long string of heavy diecast postwar freights (especially those with coil couplers) and expect your empty hopper to remain upright on a tight curve. (My 9111 derails with a light caboose behind it)
Motive power pulling capacity is directly related to the weight of the cars produced at the same time as a locomotive. A 2035 with Magne-Traction can out pull a James Gang general because the 2035 was designed to haul heavy cars and the DC #8008 JGG was only assigned 3 very light cars.
Modern locos with flywheel equipped pitman motors can out pull darn near anything from the postwar era on. Especially dual motored diecast behemoths like GG-1’s.