If you simply "copy" the trades of a professional trader, but with less money, isn't that *guaranteed* profits?
Within finance, there is interest in attempting to replicate the positions of strongly performing funds. So your basic premise has some merit. However, most funds attempt to obscure what they are doing to foil copycats.
However, what you describe has risks.

The investors you are copying may lose money themselves. In particular, there is no reason that people making videos on spreading them online are telling the full truth about their performance. Securities laws generally prohibit giving unsolicited investment advice, and professional investors are generally aware of those laws.
If you get information with a lag, you are not going to replicate their results. In the worst case, they buy before the price rise, and then recommend others buy at the higher price (allowing them to sell). This is a common feature of fraudulent stock trading schemes in penny stocks.
Even if you can avoid the previous problems, a smaller investor may not be able to trade all the instruments a larger investor can, and face higher transaction costs. If positions are actively traded, higher transaction costs (as a percentage of the portfolio size) can mean the difference between a profit and a loss.