Nature vs. Nurture, and Who's Play is This, Anyway?

I've been thinking about the ways in which the play offers commentary on the nature versus nurture issue, specifically related to the way that Guiderius and Arvinagus function in the play. Are we to believe Belarius and his repeated remarks about G. & A.'s emergent princely natures ("The time seems long, their blood thinks scorn / Till it fly out and show them princes born") ? This seems to support the accepted notion of royal lineage and the inborn divinity of kings. Furthermore, Belarius scorns the "art of the court," seeming to nearly vaunt the "honest freedom" he has lived in since his banishment. Is this just Belarius' bitterness coming out, or does he function to make a more explicit statement about the role of nature versus nurture in kingship? Is he saying the natural divinity (?goodness) of kings is corrupted by the court? It occurs to me that Cymbeline's behavior may support such an opinion. That leads me to my next question, which may seem petty or just obtuse on my part - but why is this play called Cymbeline? Is it because Cymbeline functions as an agent for the three plots (to which Innogen is more central)? His agency appears to be predicated on his poor judgment: his treatment of Innogen at her marriage to Posthumus and the latter's banishment (no doubt under the manipulation of the queen and Cloten); his willingness to engage in war with Rome (also a result of the queen's and Cloten's wishes); and finally his banishment of Belarius (apparently upon the word of "two villians"). Not to mention, unlike his heroic sons who inspire the Britons to fight, Cymbeline is described in retreat (I hear Monty Python, "Run away...run away...). Anyway, if Cymbeline is such a lousy king, why does he get the title (of the play, that is)? And in what way does this relate to my earlier question about the nature versus nurture issue?