Well, I suppose I could either choose to believe you, or the tons per mile figure published by the railways every year. Yes, actually, you can grow your business even as you chop the weaker parts off at the knees. The greatest revolution in rail shipping has been the replacement of 2/3 of box car traffic with intermodal trailers and containers. This latter business does not require branchlines, which is mut of what has been pruned. The other great revolution has been the unit train hauling 115 ton cars of coal, aggregate, grain, and chemicals. Rail cars have gone from 50 tons to 70 tons to 100 tons to 115 tons during the past 45 years, and trains have gotten much longer as well, with 10,000-15,000 tons in 100-150 cars being typical, as opposed to 5,000 tons from years gone by. It goes without saying that your line capacity can be vastly increased by hauling more cars in longer trains with greater payload per car even as your total number of trains falls and you reduce your mileage.
For example, the main line across Pennsylvania's famous Horseshoe Curve handles as much tonnage as 50 years ago but in half the trains and despite the deindustrialization of the rust belt. Many lines out west handle much much more than ever before, which has necessitated hundreds of miles and double and triple tracks being constructed, and with more to come.
Lastly, main lines can be abandoned because two lines which worked at 2/3 of their maximum capacity 45 years ago can be combined into one line working at 2/3 of its capacity with the increase in train size and weight.
So yes service can be increased under the circumstances present today.