The present era of design is all about relative color pie balance (as opposed to the earlier, "blue and artifacts are broken" eras). This entails making sure every color has a range of effects available to it that make sense, are not too many or too few, and don't step on any toes; that the colors all play differently and all can participate in creature combat and spell slinging alike; and that they all have strong enough cards to have a fighting chance.
That last thing is difficult, even compared to how hard the others are. There are a lot of formats, Limited and Constructed, for which the same set of cards must be exciting but balanced. And currently, red is a bit of a redheaded stepchild for EDH, being unable to carry a deck on its own effectively.
Mark Rosewater addressed the issue on his Tumblr blog recently when justchainsawthings asked, articulating the problem, "Many people believe that Red is the weakest color in Commander because burn is ineffective against a higher starting life total. I know that Chaos Warp hurt the color pie but are there plans to give red more tools to be a competitive commander color? Was Prophetic Flamespeaker a step in this direction or a one-off mythic?" Rosewater replied:
We’re looking for ways to help red in Commander but we want to find solutions that stay true to red’s slice of the color pie.
Over the past few years, expensive creatures like Charmbreaker Devils and Molten Primordial have indeed been printed partially for Commander reasons; but large creatures that aren't designated commanders have to do extra work to keep up with the big legendaries. The value of Prophetic Flamespeaker and these two is in the (temporary) card advantage they generate. Ironically, Worldfire, one of the best spells for EDH imaginable, earned itself a pretty quick ban when it was printed not very long ago. All told, a step forward for red could be giving it the capability to deal with multiple opponents at once, giving it some of blue's spell manipulation abilities that it shares in more often, or simply printing pushed red legendary creatures.