Every organisation need a strong head, someone that is bold enough to make decisions. Luca is such a man. Remember 1998 and 1999 when Italy was asking for Todt and Michael's heads? He stood by them against popular uprising in Italy through the media. And he was proven right. How many men would have made that decision.
Luca doesn't run the F1 team. Though he is briefed everyday by Todt. So ultimately he is responsible. The sytem of reporting will still continue but how detailed compared to before is unknown. But there is huge trust and respect between Luca and Todt and I am sure Todt will not step up to his new job if he does not have Luca as the Chairman, who will sort out the political issues of Ferrari. Allowing a Frenchman to have free hand in the F1 team is one thing, allowing him to run the whole of Ferrari is another issue altogether. It has a lot of 'political' baggage that may sink Luca's career. But like in the late 90's, he has visions for the future of Ferrarai and like always before he will be proven right.
So does Ferrari F1 need Luca. Yes they do. Standing up to the FIA, standing up to Bernie and standing up to GPWC. These are issues that are critical for the F1 team and these are issues that only Luca can take up on behalf of Ferrari. When Luca speaks, they listen.