6 Kilometres in Metropolitan Cities is not something that people would find difficult. Prayagraj Chheoki is 14 kilometres away from Prayagraj Junction, yet people travel in hoardes to go for their connecting train.
Yes had the timings been reversed, morning departure from Sabarmati and evening departure from BGKT, i would've agreed with your point. But here it's reaching in convenient enough timings for people to go for Mumbai Vande Bharat, Mumbai Shatabdi, Gujarat Queen or evening/night departures. They don't have to stay overnight, which would've been the case had the timings been reversed. This is actually beneficial
Also...
more... Vice Versa is true for people arriving till Afternoon at Ahmedabad Junction from trains like Mumbai Vande Bharat, Mumbai Shatabdi, Sarvodaya Group, Coimbatore/Secunderabad Express.
This actually gives great many options and Ahmedabad doesn't have intense traffic issues like Pune, Mumbai or Bengaluru yet.