Metal guitar rhythms and chords are not just power chords, they can be suspended chords, power 4 or inverted fifth 5th chords), altered power chords b5 (diminished), and many other guitar chord types as well. Although these types of power chords do play a big role in the metal chord. A complete Dominant 13 chord for example is not a classic metal chord.

Metal chords can actually be very flexible in their use and therefore used as the metal rhythm for advanced metal soloing over because many times their actual makeup is a guitar power chord, or like that in concept. So aside from for example speed soloing that you may hear over metal chords, there is often a lot more theory being used in regards to the actual soloing and chord changes.

While lowered guitar tunings may be sometimes used on the instrument and various effects, remember that does not have anything to do with the metal chord. These will give a different sound, heavier sound, also depending on the amplifier used there may appear to be more to the metal chords structure. But when it gets down to the chords themselves, they are generally configured with fewer chord tones often just two.

You may or many not be surprised to know that many of the great guitar metal players know a lot more about music theory, advanced chord structures and other styles than you ever realized. Most times they are players who have studied the guitar in depth and then have focused on the metal style for personal interest. Get the most our of your learning with a guitar metal method of learning that is really a guitar course in playing that will give you the metal playing skills and knowledge as much as any other style.