I don’t know much about the things that happened during Sir Alex Ferguson’s departure but the club has suffered and struggled since then which certainly tells that the management style and strategies have not been efficient and effective since then. The Glazers are the real problem gor Manchester United for their poor management style.
I think Ronaldo in that interview quite simply laid out what happened to United. The club just fell behind the times due to weak management - while everyone was developing, improving infrastructure, etc. United were trying to be successful on old baggage. In a highly competitive sport like football (especially in a league like the Premier League where there are a lot of moneybags) this was suicide. And I don’t even know whether the Glazers can be blamed or not, for example, Bayern made the similar mistake, but they have no competition in the Bundesliga, but on the European stage they are no longer the elite.