Why would it hinder him to go to FCW if they think he has it? If he's not successful in FCW, then he won't be in the WWE. Better to find out then as opposed him going to straight to WWE and failing. Braden Walker.
Like I said earlier, the WWE is running low on talent to put in their NXT season 3, and Black certainly is a worthy candidate of being on the show.
He could cut promos in FCW and then go to NXT if need be. If he sucks on the mic when he is in FCW, what's going to be any different if he's on NXT? Baby steps.
You yourself said he was average on the microphone, and if they gave him a gimmick like Chris Benoit had, which was a guy who would show it with his actions rather then his words, he would be widely successful. If you have a great wrestling ability you can pass with only being average or possibly being below average on the microphone.
Punk didn't find his niche until three years into his WWE career. Cena and Orton did it in a much faster period of time. If Cena couldn't freestyle, he maybe wouldn't be here today.
Punk may not have been his best until last year when he turned heel, but that's not his fault, it was the booking. And I'm pretty sure he became ECW Champion in 2007 and World Heavyweight Champion in 2008, so it's not like he was treading water and doing nothing in the WWE from 06-09.
Edge was the only one to find success right away due to him being in a tag team with Christian.
Triple H made his WWE debut in early 95, didn't get a real program til the next year, and won the IC title a few months after that. Not a great deal of time. And Mysterio won the CW title in his WCW debut and was the 2nd ever WWE Tag-Team Champion, just debuting in June of that year. I think that's some early success.
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Closing: As I've said before, it wouldn't hurt the WWE or Black one bit to put Tyler in this next season of NXT. Their talent is running thin in FCW and the crowd could get behind him like they did with Danielson and Kaval in the seasons previous. You don't always need to be a great mic worker to get to the top of the totem pole. Chris Benoit, Jack Swagger, Rey Mysterio, and Batista are clear examples of this. Black will impress fans with his in-ring work and can pass with average mic ability. If they have NXT, why not put guys who are deserving to be on the show on it? Black is clearly deserving and should be on the next season of NXT.