The fore-stitch is the foundational mechanic which all other stitches are formed. While a fore stitch is primarily used as a basting stitch (if looking at it as mearly a running stitch) you use the same principles in its formation as you would a felling stitch which is a fore stitch thats formed off axis or even a padding stitch which is a fore stitch thats taken on a different plain. So to this, is why I feel the fore-stitch is the most important to master. It also has the benefit of training muscle memory, stitch spacing and can be easily removed for more practice. Im really just going to make a YouTube video on the principles of needle work.
I suppose it's the most basic forward stitch, yes. A fell stitch is more like a padding stitch in the way it is formed (I see you alluded to this). There are other similar stitches, but they depart from being running stitches in the way they anchor themselves and behave under tension. If we were going to be doing the business of identifying the 'foundational mechanic' it would probably be the act of how one pierces the cloth with the needle. I'm not too worried about all that.
What I was asking was if, beyond basting, anyone uses a running stitch for anything else. Since it's extremely weak as a permanent stitch and gathers too easily, I assume not. It's useful for gathering as another sort temporary stitch. It plays it's part.