I think Hobbes has hit the nail on the head - ask 10 different cyclists and you'll get 12 different answers. There's a lot in your example route that I personally wouldn't consider "easily passable" or "a pleasant route". That's not to say I'm right and you're wrong, or vice versa. But it's not the sort of cycling I like to do.
Local authorities are risk-averse, largely because people sue at the drop of a hat these days. I was once involved in a signposted route project where the local authority refused to countenance a cycle route going north-south across this junction -
https://goo.gl/maps/aztYr57n4oZDZCDz5 - because they thought the crossing was too dangerous. If they're not happy with that, they are never going to agree to sign the A30 from Shaftesbury to Salisbury as a cycle route.
I like cycle.travel's style of routes which is why I built it like that! I'm sure it'll be too winding and indirect for you. That's fine. There are other route-planners available with different takes, or you can customise your own preferences using something like brouter.de. Just get a battery backup for your phone, or an app that doesn't gobble battery, or a Garmin with good battery life (an Edge 530 will do 20 hours happily) - it's a solved problem.