Technically yes, we can say that all graphical editors rely on linear algebra for various purposes. It's just that not all of the problems are obvious to anyone who starts developing something like this. That is why I decided to share some of the challenges I had encountered from a math perspective. I guess the main point I wanted to make is how matrices simplified the calculations for me even though I already used linear algebra.
Also another point is that, if you rely on SVG for rendering you could get away with just the code without thinking too much about the math involved. For instance if I wouldn't have introduced object hierarchy, I wouldn't even have to bother with math at all. SVG can take care of all the transformations, I wouldn't even have to know that matrices exist and that I could use them in svg objects 1-on-1. Dragging an object without a hierarchy would also propably be much easier, all I had to do is to change the translate(x,y) inside of the svg transform attribute.
I had a similar experience: I built dragging and handle resize, then later added rotation via a bit of trigonometry. Each operation worked fine separately, but if you tried to rotate and then resize, unexpected things happened. I left the bug for years, thinking I needed to come back and just add a bit more trigonometry to get rotated resizing working. When I finally came back to it I spent quite a while hacking at it before realizing that matrices were a much better way to describe the solution.
Also another point is that, if you rely on SVG for rendering you could get away with just the code without thinking too much about the math involved. For instance if I wouldn't have introduced object hierarchy, I wouldn't even have to bother with math at all. SVG can take care of all the transformations, I wouldn't even have to know that matrices exist and that I could use them in svg objects 1-on-1. Dragging an object without a hierarchy would also propably be much easier, all I had to do is to change the translate(x,y) inside of the svg transform attribute.