No, it's not "inarguable". What the paper says is that some funds in the extreme right tail are able to demonstrate a modicum of skill, meaning they do better than pure randomness would suggest. However, they do not do sufficiently better to consistently generate four-factor alpha net of fees. In other words, they do not do sufficiently better that you could invest in one and have a higher expected return than you would get investing in a passive fund with similar factor exposure.

The bare fact that certain funds or managers have averaged 20%+ over whatever time period is irrelevant, as that is absolutely expected due to randomness alone. It has no predictive power over the ability of those funds to generate future alpha, regardless of what intuition suggests. Again, in other words, investing in a fund that has consistently outperformed in the past does not increase your expectation of outperforming in the future. In fact, it is more likely than not that you will still underperform a low-cost passive fund with the same factor exposure.