Joe Blanton Is Awesome Now, Apparently
This is an oversimplification, but to be a successful starting pitcher in the current era, you have to maintain some reasonable level of effectiveness for something like 25 batters per start. If you can’t pitch into the sixth and seventh innings with regularity, you aren’t going to remain a starting pitcher for very long. In the past that number was higher and in the future it might be lower, but if you don’t have the tools to remain effective for two or three turns through the order, you’re destined for the bullpen.
Pitching is multidimensional, which means that in order to pitch well enough to remain a starter, you need some combination of skills which push you across that threshold. Command, endurance, and stuff all play into the equation. Command is the ability to throw your pitches where you want them and endurance is the ability to maintain your command and stuff over multiple repetitions. Stuff is more complicated because it is partially a measure of individual pitch quality (defined in many ways) and the number of pitches you have at your disposal.
In other words, if you have average command, decent endurance, and the world’s greatest fastball, you can probably get by if your other pitches are only okay. But you can also get by without a great fastball if your command is elite and you have three solid pitches. There’s no single path to success.