I'm going by the local history books I read about the building of the Far North line and also the Wick-Lybster Light Railway and the debate of the reason why it followed the route it took rather than the direct route.
Though my personal thought that the direct route would have had too steep a climb out of Helmsdale to keep to the coast, and taking the valley inland gave the line of least resistance.
Yeah, that's what happened. It's a pity that they couldn't serve places like Latheron, Dunbeath and Lybster on the direct route, but they just couldn't afford it - I'm not sure it would have been worth it based on the line's usage today.
You may also know that they were once going to extend the light railway south from Lybster to Dunbeath, but that never happened. And they were going to have all sorts of other lines... as well as the Black Isle, Strathpeffer, Lybster and Dornoch branches, lines connecting to the FNL and also the Kyle Line were planned from Conon Bridge to Cromarty (six miles were built at the Cromarty end, but never finished due to the war), Garve to Ullapool, Clachnaharry to Lochend (at the northern end of Loch Ness), Achnasheen to Gairloch, Poolewe & Aultbea, Culrain to Lochinver, Lairg to Laxford Bridge, Forsinard to Melvish & Portskerra, and from Thurso to John O' Groats. There was even a plan for a line linking Thurso to Scrabster - a big shame that
that never happened, it would be worth doing.
The Highland Railway by H. A. Vallance is a great book - and it details these plans as well as others. Can you imagine that they wanted to build railways on Skye and on Lewis/Harris? There were plans for lines from Kyleakin to Broadford and Torrin, from Isleornsay (near Armadale) to Broadford, Portree, Uig and Dunvegan, and from Stornoway to Breasclete and Carloway! The latter two propositions we from the Hebridean Light Railway.