As a counter-argument, you usually need to read a lot into the reported numbers, for example read the 10K notes for multiple years in the past. That's the only way to know that the 3B in assets showing up on the balance sheet for "goodwill", to use one easy example, are not really worth 3B. There are many more-nuanced factors that work alike. The reported numbers are what the accountants think might fly under GAAP, and the accountants work for the CEO, who has a say in the accounting "intent".

To test whether markets are perfectly efficient, just look for large movements over time. If a stock goes up 20% in a year, the market might have undervalued it last year, or is overvaluing it this year. It's unlikely the it was correctly valuing it at both times. In the absence of a Covid-19 pandemic, act of god, etc. of course.

You could say that the market just takes "investor sentiment" into account, and is therefore still efficient. But value investing is a strategy that looks for misplaced investor sentiment and exploits it. If that's the way you define an efficient market, than I'd say an efficient market is no obstacle to a value investor.