I am an older engineer and I would rank myself 6-7/10 in most aspects of my work, even if I have architected and built some trend-setting systems in my corner of tech. I have never seen a junior score themselves so low on average.
My experience is also that companies that care about these things (where hires are mainly filtered by HR and not SWEs) tend to build very mediocre teams. I am probably old enough to eschew the whole resume padding or prettifying thing all together. My last resume was written in Notepad, and it worked just fine for its purpose.