What kind of assets are you buying? I thought most assets were character models and such but sounds like you buy assets with actual functionality. Do you have any examples?
Especially for a software engineer, there's of course always the fantasy of coding everything on your own. I might not get a platformer system because that seems "fun" to implement, but shaders often feel so beyond me that I'd just rather get someone's optimized shader.
That's basically a 2D / 2.5d game framework.
Nothing from the Asset Store is essential, but it would take much longer to do everything yourself from scratch, as well as being difficult to learn how to do everything yourself without examples to experiment with.
> The Corgi Engine is recommended by Unity as part of its 2D Essentials Pack.
Maybe I read too much into it.