Then again, the classic "mob-boss/godfather" modal is someone offers and hands out protection and gifts to those who are weak, kind of Kringle like. In turn they are loyal and pay tribute in various ways, except if you get on the "naughty" list your can get a hell of a lot worse than a little coal in your sock.
Depends how the sock full of coal in then used by this version of Santa’s ‘little helpers.’
One telling thing is that Marcone has never been into succession planning, that much is clear from Small Favour, he is aging out and aware that Harry still has centuries ahead of him. A coin (or a Mantle) allows Marcone to think genuinely long term, something he alluded to in Battle Ground. His two objectives has always been (1) get more power and (2) maintain power. The coin (or a Mantle) achieves both objectives, as soon as he judges that it doesn’t or there is a better alternative he will drop it, he is beholden to no one.
Taking up the Kringle Mantle doesn’t mean that he would necessarily swear fealty to Mab, but would free him from the coin, he could decide to go Wildfae, he genuinely respects Mab and likes working with someone with such a cold logical mind akin to his own (Mab and Marcone are very similar personalties) and Marcone is learning a lot from her, but even so he would not want to be a Vassal. He would take the Mantle only if he could be free, and Mab currently owes him big after the battle of Chicago. He would I think be an ally rather than a vassal.