To answer your question, the Career mode in Live does not feature microtransactions, it uses an XP system.
As has been stated before,since the success of GTA5 Online Take 2 Interactive games have been increasingly designed as a platform for the sale of microtransactions. They will continue to push the envelope until enough people get tired of paying full price for a game with the economy of a "F2P" mobile game and the "VC Bubble" finally bursts.
Hopefully this comes sooner rather than later.

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