I think UE4 and its Blueprints are very nice and cool but with regards to how stuff might or might not scale I feel compelled to link this site called UE4 Blueprints from Hell haha https://blueprintsfromhell.tumblr.com/
Of course anyone can make spaghetti in any language, text-based or visual, so don’t think of that site as “proof” or anything. Just a little bit of entertainment that’s all.
I don't know blueprint, but I'm wondering if after some time using it you begin to pick up patterns from looking at zoomed out code. One thing that strikes me is that each of these "nightmare" examples has a very definitive and recognizable form. There are certain structures that one can pick out and recognize between diagrams. It reminds me of being able to discern nested loops and long switch statements in traditional text code minimaps. It might be the case that these code maps look like a spaghetti mess to the untrained eye, but the variety of structure in the code allows skilled developers to zoom in on a bit of code the way you can zoom in on your house in Google Earth without any help.
Of course anyone can make spaghetti in any language, text-based or visual, so don’t think of that site as “proof” or anything. Just a little bit of entertainment that’s all.