Maybe my view is warped because I don't work for an SV startup, but I would consider anyone with less than 5-10 years "entry level". I rarely see job ads for anything except interns/entry level and "senior engineers". Someone with 3-5 years of experience probably has some job security but definitely doesn't count as "senior" in my mind.
I don't think it's just SV, I've seen job postings in Boston for 3+ years experience and it was listed as a senior engineer. I think it's because many companies try to use titles as compensation. I've gotten the "senior engineer" title 3 times in my career. Two of those times it was given to me in the same conversation where I was told there was going to be no raises that year.
“We’re rewarding you this year by making it easier for you to find another job” sounds insane when you say it like that, but that’s what they did!