Aubergine, sorry to see you so angry. Believe me I can feel with you. I played the game a lot (also before I joined Urban Games) and I know this can be a problem.
I absolutely agree that the slow growth versus the fast decline is far from ideal and is something which belongs on the to-do list.
But otherwise I also have to say, that apart from a stuck train I rarely have the problem that I go into the “death spiral”. Usually it takes a couple of days or weeks until the industries update and recognize changes in the lines.
When changing a train setup I try to do it one by one (usually I run multiple on a cargo line to have a higher frequency) or I use the auto replacement tool to increase the capacity over time. Also I never use the “wait for” option – I tend to let the cargo stations “overfill” a little bit.
But of course that is just my personal playstyle …