"In that sense, GDPR has not curbed US giants' power. So what did GDPR achieve in practice?"
I don't think GDPR was ever about about curbing tech giants' power nor changing their business model. It was always only about protecting the personal data of EU residents.
Assuming the tech giants' business models do rely on indiscriminate use of user data, and that the GDPR does interfere with that, it applies only to EU residents, which I assume comprises a relatively small market-share. For a fundamental shift in business model, the US would have to adopt similar measures for its own residents, but the political climate would not allow for that, I don't think.
I don't think GDPR was ever about about curbing tech giants' power nor changing their business model. It was always only about protecting the personal data of EU residents.
Assuming the tech giants' business models do rely on indiscriminate use of user data, and that the GDPR does interfere with that, it applies only to EU residents, which I assume comprises a relatively small market-share. For a fundamental shift in business model, the US would have to adopt similar measures for its own residents, but the political climate would not allow for that, I don't think.