Re: Why my neck of stock humbucker of Ibanez RX 180 Japan sounds thin and weak?
"Thin and weak" is highly subjective. The pickup itself might be much less out put than the bridge. Next you have a 2-wire (+ ground) pickups so the two coils (of the humbucker) are wired as one meaning you always get both coils on or off (you can't split them, etc.). So with the switch in neck-only position both coils of the neck PU are on... touch the coils with a small screwdriver and you'll hear if they're on. Likewise see if other coils are on (which they should not).
Lower the bridge PU, raise the neck PU a bit and see if it balances things. I wouldn't jump to conclusions that this is a wiring problem.
You can (should) quickly measure the relative output of each PU with a multi-meter to compare resistance (more resistance, more output) of the bridge vs neck. One PU might be 5Kohm the other 10Kohm (more output) let us know.