The most common diesel-electric locomotive today has 6 drive axles. The big steam locomotives designed at their twilight sported 6-10 drive axles, and the most famous and successful of them (the 4-8-8-4 Big Boy) ran 8 drive axles. Mechanical linkage of drive axles isn't what killed the steam locomotive.
Mechanical linkage for multiple direct drive external combustion engines that can operate at 0 rpm is far simpler (the drive axles are basically the crankshaft) than for a single internal combustion engine that must maintain a minimum engine rpm and has to be geared down to axles that are riding on a bogie that pivots separate from the deck of the engine.
To take advantage of the increased efficient of an internal combustion engine you'd need a lot of mechanical complexity unless you go hydraulic (solidly defeating most efficiency improvements) or electric.
