Learn Spanish (Latin America): ¿Será inteligente? Más bien es manipulador. - Could he be intelligent? Or rather, manipulative?

In this sentence, más bien is a discourse marker used to correct or refine a previous thought. It translates to "rather" or "more like." Here, the speaker is rejecting the idea of him being intelligent and offering "manipulative" as a more accurate description.

Could I use mejor dicho instead of más bien here?

Yes, but the nuance is slightly different. Mejor dicho (literally "better said") is typically used to correct a slip of the tongue or clarify your own words mid-sentence. Más bien works perfectly here because the speaker is intentionally contrasting two concepts, rejecting the first option entirely in favor of the second.

Why is the future tense será used if they are talking about what he is right now?

This is the "future of probability." In Spanish, you can use the future tense to express wonder, uncertainty, or a guess about a present situation. ¿Será inteligente? essentially means "I wonder if he is intelligent?" or "Could he be intelligent?"

Why isn't there an article before manipulador?