Are Tour Player's caddies easily a good player themselves?

Halo Bro(s),
Not sure if this has been discussed on GR forum before, but I always wonder if Tour Player's caddies are good players themselves. I appreciate if someone share their view. Ok we have seen it on TV that...

Phil Mickelson's discussed at length with his caddie Jim McKay (or something? not sure if i got the name right) before executing a shot, and I hv even seen a soft arguement between them before a shot was executed. Next, Steve Williams at time seem to be telling Tiger Woods what to be done with the next shot approaching green. Okie, someone told me that most caddies get themselves familiarize with the Tournament course before Day-1 to enable themselves to so call "know the course better" than the one actually hitting the ball.

Some hear/say from here/there suggest that these caddies know well what their masters are capable and incapable of, therefore they can advice - but I don't quite buy it completely. I believe some of the world's top players know themselves better than anyone if they're capable of hitting and carrying a shot over 200 yards from a deep bunker, across a yawning pond, against headwind with a 6-iron, while landed the ball 5-6 ft next to the hole!

So, apart from ensuring their master's bag has the right number of clubs (<14), right color of Sharpie to enable their master to sign autograph, enough sandwiches with the right jam to share among them for the round, grip clean & tacky enough for the next round (read too much magazine on WIMB liao...), it seems apparent that their job is more than carrying the bag. But again back to the main topic, if these guys are actually giving advice to their master or even arguing certain shot decision, in this instance... Mickelson & Woods, wouldn't these caddies should rightfully possess some level skills and knowledge themselves to be able to advice or "argue" with some of these world's top players? Suppose the answer is yes (they are skillful player themselves), then why don't they ditch their master's bag aside and turn pro themselves to push some luck on Tour?

Well, having pick-up this beautiful game not too long ago, I am not sure if I've posted a valid question here, but if you do understand where I'm coming from, I'm really keen to hear what some may say.

There is a difference between being a good player and being a Tour player.

Steve Williams is a 2 handicap but when he plays with Tiger he still gets 10-12 strokes.

Fluff and Jim McKay (bones) play to about 6, not enough to win money..

If you love golf, and make a better living caddying than playing, you are still doing what you love, or at least you are still around the game....