In my personal experience, what the book refers to as "becoming the arrow" is very different than what you're describing by "indexing the tip of the broadhead".
You are correct in that the method YOU are using, referencing the broadhead tip against the target, is NOT becoming the arrow, and it IS indeed using a "sighting system".
While I don't buy into the whole voodoo hippy "become the arrow" jargon, I do understand the philosophy.
Personally, when you become ultimately comfortable with your bow, you won't need sights, and likely can shoot from nearly any position and make contact.
When I was a kid, I shot fiberglass wally world special bows with wooden arrows all the time, for rabbits, squirrels, birds, etc. My dad taught me to shoot these bows by focusing on my target, and just letting the arrow hit it. At first, I practiced similar to how you are, by referencing the tip of the arrow against the target, but with practice, I learned to shoot by "feel". Now I simply focus on the target, and let the arrow hit it. I just "know" how to hold the bow for it to hit the target.
I can't say the same for my new Bowtech Destroyer 350. Even though I can shoot my new bow MUCH more accurately while using sights, if you take the sights away, I'm a mess. I'm just not nearly as familiar with how it shoots as I was with those old fiberglass bows.
Using the ball player analogy: Young ball players practice throwing over hand in the same form over and over. They use the same form, and can deliver very accurate throws. HOWEVER, if they're forced to throw from a different position, like a backwards flip, or a spinning toss back to 1st from left field, their accuracy will suffer greatly. On the other hand, pro ball players can make these "off angle" tosses with amazing accuracy, some out field players are even famous for "no-lookers", where they can field the ball and throw the ball accurately back to home plate without even looking at their "target". They just KNOW where the ball is going to go.
Similar to the ball players, or my cheap fiberglass kids bows, I'm also able to shoot "instinctually" with my first rifle, and my 2nd handgun (which I shot a LOT more than my 1st handgun, which was a Ruger Super Blackhawk .44mag).
My Marlin 99M1 was a hand-me-down from my grandfather to my father, then to me. My father had lost the rear sight when HE was a kid, so all I had to go by was the front sight. That is, until the FRONT sight fell off when I was in high school. I took that rifle EVERYWHERE, and even though the front sight fell off, I was still able to shoot it incredibly accurately. Surprisingly, I still shoot that rifle to this day almost as well as I shoot any other open sighted .22lr rifle, but without any sights, just by looking at the target and letting the bullet hit it, whether it's a shot on a running coon in front of our hounds at 50yrds, or on a rabbit in a pasture while hanging off the back of our coyote wagon, it just HITS what I tell it to.
Also, I'm able to shoot my Ruger Mark II .22lr pistol very instinctually. I bought it when I was 16, and it's basically been attached to my hip ever since. In high school and college, I'd go through at LEAST 100rnds a week, coon hunting, rabbit hunting, plinking, shooting mile-marker signs out the window of my truck while I was driving home from school, throwing pop cans in the air, etc etc. Whatever condition, from the hip, aimed, light, dark, moving targets, awkward footing, or at a dead sprint, I can deliver hits with that pistol. I just look at the target, and deliver the shot.
For whatever reason, I have 2 newer Marlin 60's WITH sights, and several other Ruger Mark II and Mark III's, and I can't perform the same shots as I can with the "familiar" weapons.
Now, all of that is fine and dandy, however, when you are after utmost accuracy, you NEED to use sights. No matter how familiar they are with their bow, competitive archers still rely on their sights. These guys could very likely "instinctually" toss an apple in the air at 10yrds and hit it without sights on their bow, but when it comes to delivering precision strikes, the sights offer MUCH better control.
If you're able to shoot enough to be able to shoot your bow instinctually, then when you combine your familiarity with your sights, you'll really have a winning combination.