Is evaluating stocks just a loss of time if the stock is traded very much?
Not at all!
Making sound investment decisions based on fundamental analysis of companies will help you to do decide whether a given company is right for you and your risk appetite.
Investing is not a zero-sum game, and you can achieve a positive long-term (or short-term, depending on what you're after) outcome for yourself without compromising your ability to sleep at night if you take the time to become acquainted with the companies that you are investing in.
How can you ensure that your evaluation is more precise than the
market ones which consists of the evaluation of thousands of people
For the average individual, the answer is often simply "you probably cannot". But you don't have to set the bar that high - what you can do is ensure that your evaluation gives you a better understanding of your investment and allows you to better align it with your investment objectives.
You don't have to beat the professionals, you just have to lose less money than you would by paying them to make the decision for you.