I have tried the paint and gimp routes,
😱
Man, MS WORD features block diagrams, full of shapes that might be connected to one another with adjustable lines and it will be far superior tool to either of these abominations…
There are also countless tools that might help you, that are either dedicated to this task, or simply useful enough to get the job done.
It often takes a different pair of eyes to see the hidden potential. 😎