The "steam vs diesel" debate has been raging on for at least 3/4 of a century now. There is no single answer that one or the other is better or more powerful or whatever.

In general, though, steam's greatest advantage is at speed, where the mechanics and physics of external combustion, evaporative expansion come into play. In other words, steam engines excel at pulling heavy loads at speed. And therein lies the weak point of steam engines, and the advantage of diesel. You need a lot of low-end power to get a train moving, and the inherent torque advantages of electric traction win out here. That's why, a UP Big Boy 4-8-8-4 steam engine (approx. 6-8k hp) might pull into a yard with 120 cars in tow, and then a pair of 1200 hp diesel yard engines walk off with the whole consist to switch it. They've got the low speed advantage over steam.

Now keep in mind that that is just a very basic comparision in general. There are lots of specific examples that could be cited to try and change the argument.

The real reason you don't find steam engines hauling trains today is not only the low-speed pulling disadvantage, but also the maintenance costs. Steamers, as John said, typically ran only a day or two before needing significant servicing. Diesels typically run months before needing major servicing. And the ability to couple up many diesel locomotives and run them as one by just one crew really helped spell the death knell for steam in a competitive environment.

John said,
"ONE 1945 steam locomotive can pull 150 loaded coal cars.
One 2008 diesel locomotive can pull 25 loaded coal cars."

Don't be fooled by this argument. The cars typically found in steam days generally weighed only around 75 tons loaded. Modern coal hoppers, fully loaded, weigh in around 135-150 tons (some grain hoppers are designed for total weight of 158 tons). For relatively flat terrain, a typical coal train these days runs somewhere around 135 cars, 15k-18k tons, and is hauled by just 2 diesel-electrics (8800 total hp or so). A single Big Boy steamer hauling 150 1940's-era cars of 75 tons each is just 11,250 tons. And I really doubt a Big Boy could pull 150 loaded coal gons. Maybe 150 boxcars averaging 50-60 tons each, but not coal.

So, last time I checked, 135 divided by 2 was around 68, which I do believe is more than 25.

Back to the hybrid topic, there are some switching locomotives known as Green Goats that are basically large battery powered electric engines. They have a relatively small diesel engine that runs an alternator used to charge the batteries. They work well when used for switching, because the typical railroad switching process involves a lot of starting and stopping, and a lot of stationary time. The diesel is able to keep up with the battery charging as long as you use it this way. You couldn't take it out on an over-the-road train because you'd exhaust the batteries before too long. The Green Goats were designed this way to be both fuel and emission efficient. Instead of a large diesel engine idling a lot, accelerating and decelerating, with the resultant poor exhaust emissions, you get a smaller, fuel efficient engine running at a much higher efficiency range.

GE has recently demo'ed a hybrid road locomotive that basically is similar to a conventional diesel electric but with additional battery capacity that can be used as traction power. Diesel electrics have had dynamic braking for years, in which the traction motors were used to generate power while going down long grades. The generated power was simply wasted as heat through grids, essentially just a large toaster (some later models of GE locomotives were even nicknamed "techno-toasters"). The hybrid locomotive is an attempt to capture and use some of this energy just like your FEH does. It may not be a lot of captured power at this point due to battery design, but as you well know any that is captured and then reused to provide tractive effort is better than wasting it as heat.