This is false. People invest on many year horizons all of the time when they believe in the company. If there was good evidence that having an average tenure of 5+ years was a great boost to the company, people would clamor to invest in companies like that.
This was basically Google’s entire pitch when they were an early public company. Happy employees == great things. I remember when 60 minutes or dateline did some special about google before 2010 and people were floored by how good the employees got it. However, hiring standards relaxed and now google is slowly rotting from the inside to realize it’s the new IBM.
Long tenure alone is absolutely not an advantage. It’s very easy to have a bunch of dead weight that just looks like they know what’s going on.
So back to your point about experience mattering. That should show up in customer satisfaction, project turnaround speed, success rates, etc. Otherwise it’s pretty meaningless. And guess who already measures those KPIs…