G/E civ 12 turn to reach Matrix + 8 turns to build 1 Invention Matrix
Neutral 8 turns to get NLC + 12 turns to build 1 NLC

Not sure how you managed to get the 12 turn to reach matrix, 8 turns to get NLC, if you are talking about the research effort needed this depends on how much research you are using and cannot be compared directly.
If you consider production alone (without taking into account that invention matrix cos 1,000 more) Let me show you how it should be done.
In the end the neutral is producing 6 RP more than G/E 
You stopped too soon and missed out the first step as well.
It is true that there is a point where you have completed 1 NLC and 1 Invention matrix and temporaily, the NLC side is 6 RP ahead, but this is more than counter balanced by other periods where
(1) There are 0 NLC vs 1 invention matrixes , where the NLC side is a whooping 16 RP down per turn
(2) There are 2 invention matrixe vs 1 NLC, where the NLC side is 16*2 22 = 10 RP behind per turn!
(3) Not to mention the last part where 2 NLC vs 3 invention matrix the NLC side is 4 RP behind.
Let's call
(0) The period where there are 1 NLC and 1 Invention matrix , where the NLC side is 6 RP ahead.
If you do the math you will find that
The period where (1) prevails is as long as (0).
Given that (1) is 16 RP difference per turn and (0) is only 6 RP this alone means the NLC side is inferior in each cycle.
of course we also have this...
The period where (2) prevails is 2 times as long as (0).
Obviously the slower you build these improvements the greater the disadvantage to the NLC side, which again proves my point that NLC is not a early win strategy.
It is not more bang for the buck. Its better use of avalible recources  IE LAND 
My friend you just restated what I said.

Of course, NLC really comes into its own in the later stages where real estate/ tiles becomes a premium.


Yes, that's right, you actually get more bang for buck for Invention matrixes (altoigh you need 1,000 RP more which isn't a lot really) , assuming you have room to put the required number of invention matrixes.

See the part after 'assuming....' , the point is NLC is not something that is effective until middle stages of the game where tiles become scarce. Early on it's actually very bad. Don't believe me? Try researching straight away from xenoethics and then to NLC and see what happens. Early on NLC won't be powerful, because the G/E race if he intends to chase a research based strategu can match and temporaily exceed you on RP with invention matrixes until the tiles start to become scare.
Don't get me wrong, I fully understand the power of NLC, having won using that strategy at all difficulty levels except sucidial which I haven't tried yet.
What I'm saying is, using it requires some skill because its effects kick in only later, when planetary tiles starts to run low. Typically , you have to keep the AI from attacking you (at higher difficulty levels) something a human opponent is unlikely to allow when he sees you using tons of NLC. In fact, I suspect the power of NLC is also due a large part to the other neutral bonuses (instant upgrades for sure) rather than from the stats of NLC.