I dont think it's unreasonable. Like any standard, it's imperfect, and shouldn't be followed mindlessly. But it has some basis in reality, in that most people get better at their job the longer they do it, and few people get worse.

I think we should be aware of the fact that we're reading an accounting of the story from one viewpoint, and hiring/levelling decisions are usually not shared in depth with people who don't need to know. And most people are bad at judging how well they did on interviews.

Saying they didn't have enough years of experience may have been the way the recruiter decided to share interviewers' feedback that they seemed inexperienced.

Or maybe it was a negotiating tactic, and the company expected the candidate to push back.

Or maybe it's a simplistic metric the company put in place to cope with their rapid growth over the past 2 years.

We can only speculate.