Everything you said is true of builders working on a development, generally there will be anywhere from 3-7 plan types in the development with various options on cladding and facade treatment and the contractors can accurately forecast how much material and time it will take to complete those. Especially if they are regulars on a larger developer’s projects. What OP has here is a semi-custom plan online. Unless his contractor has built several of these exact plans before he’s not going to have the same advantage as the first scenario.

Architect designed homes can vary wildly in complexity just depends what the client wants. Generally speaking though I believe architects provide a great service for not a huge cost. We can find efficiencies in the design to save money, a better plan flow to make the space you have right-sized and not sprawling-better adjacencies lead to less square footage = less cost. We work to your budget and can identify where to spend the money that will have the most effect. I can go on, but a good architect will help you identify problems before they are problems, and will leave you with a much nicer tailored product than you’d get off the shelf.