How can I make this more readable? I need to change the space around the words, but do not know how big to make it

I’ve got a big strategic road map that I created in Visio. I know that Visio is not the ideal choice for all elements of this project, but it checked most of the boxes without having much downside. However, one downside is that subtle changes are time-consuming because everything needs to be manually adjusted.

So I have created this thing and I have feedback that it’s hard to read. Feedback is also that opening up the space around the text fixes it. So I want to add space, but not too much, because economy of spacing is important.

Are there guidelines for spacing things like this? Ratios or something?

Rather than just guess, I prefer some sort of guide if one exists. A rule of thumb or something?

Should I maybe also increase the vertical spacing between elements?