[Big Dave]

Why don't you check out the market for mechanical drives and see if you can find one bigger than 1300 HP? You won't find one. These are occasionally used on little 500 HP industrial switch locomotives but could never venture out on the mainline with the big dogs. No gear would stand the "buff" (fore-and-aft) pounding a train dishes out. Even in big mine haul trucks the standard is now diesel-electric.

Keep in mind on locomotives weight is not much of a limitation. Most locomotives use scrap iron and concrete to ballast them up to the commercial weight. So the weight of diesel-electric drive is no big deal.