I do agree with the OP here, not so much that Bolt looks heaps better but it is obvious its more legible. There could certainly be some effort taken so that BP is cleaner by default, the spaghetti is not really a big issue as code will always end up that way (even c++) because of the complex nature of interactions between objects/classes.
One thing I like here in the Bolt Alpha picture are the compact nodes, it could be nice if BP had an option to have large or compact nodes depending on preference, I personally feel like the expression nodes still take up too much space for what they are because when making complex expressions they get unwieldy pretty fast and you want people to focus on the expression not the layout. The branch node just seems huge for the simple functionality it provides, a seasoned programmer will know what the boolean is for, what each of the flows are for, to me it seems more pertinent to show what the node is doing rather than teaching people to code through lego blocks. Lets take the set node as a comparison to the branch, see how its flow enters up near where it says set on the header where branch, functions and events all do it lower, shifting the branch name to the center and down slightly would allow the same thing and it would line up with the set. Im just of the opinion BP tries to tell you too much information that you dont really need to know, information which could be expanded upon in non-compact nodes or mouse overs. Target-Self could be totally omitted as an example and added back similar to structure node which allows you to modify the elements or again on a non-compact node.
The colour contrast is clearly better in the Bolt pictures too, the red of BP is too deep and could definitely be made brighter so it doesnt sink into the background, the pink is better because its brighter. The grid also makes the white/grey flows sink on the BP where on the Bolt one you can see it popping more which is useful, I dont think the OP is suggesting make everything look like pastel vomit just make it easier on the eyes. Sure BP has some customisation under the hood but since the visibility is largely cosmetic it shouldnt have much impact on the BPs from a functional standpoint which makes this a modification with fewer legacy issues.
As a person who has been using BP for many years Id like to see it improve, the functionality has come a long way but I feel like visually it could still use some work. I feel like a fresh perspective is sometimes the most honest as they dont have the same bias, that mentality of “this is how we’ve always done things” 