Look at the Facebook page re the 1856 surveyed route, which would serve Gatehouse at the town's north-eastern periphery.
Re bus services.
Dalbeattie to CD by bus 18 minutes , train 6 minutes.
Dalbeattie to Dumfries by bus 24 minutes, train 15 minutes.
CD to Dumfries by bus 30 minutes, train 22 minutes
Gatehoues to Dumfries by bus 1 hour, train 35 minutes.
Oh dear. You criticise posters who are rail professionals for telling you the high costs of new alignments, then you propose a new alignment yourself based on an 1856 survey. What Facebook page by the way? Why was the railway built using a different alignment from the 1856 one in the first place?
And your estimates for the bus journey times from Dalbeattie are obviously centre to centre, and for rail station to station. But the bus runs right through Dalbeattie from one side to the other, so quite a few people don't get on in the centre but at stops nearer their homes. How close to the centre would your reopened station be?
We know where Dumfries railway station is of course, and while it is certainly well within the town, it is like many stations off-centre. Buses from Castle Douglas and/or Dalbeattie have already passed through much of the town before they reach the station. So quite a few of the bus passengers have already got off. For people who want to start their journey in Dalbeattie other than opposite the station, or to go to anywhere in Dumfries other than outside the station, you need to add walking time or the time for using a connecting bus. Why do you think the passengers deserted the train for the bus originally, back in the 1930s to 1960s?
Any calculation of benefits from the proposed reopening made by an official body is obliged to take this into account. As a general rule the longer the journey the more people are willing to walk or connect at either end. But these journeys from Dalbeattie are shorter in time than many routine bus journeys.
Finally - a note of cynicism. As others have said, the Borders got their railway back as a political ploy within the Scottish parliament. As long as the majority of Scots vote Nationalist (or if they decide to return to Labour), and Dumfries and Galloway vote Conservative, there's no political advantage to anyone in Edinburgh in giving the region a railway.