Yeah, now that you mention it, it probably would be easier to just pass in an array with the dimensions. The filename doesn’t really exist as a variable prior to the resize function in the other section of the code, so you’d have to find a way to figure out what the name is GOING to be before you can even check to see if it already exists.
I tested it via a debugging function I have in EWWW Image Optimizer, just added a couple extra lines in on my local dev install of WP, and then I could see that every time I refreshed the page, it was sending an image through the WP_Image_Editor functions that EWWW hooks into.