Ok so lets play this game. I'll name some stars that weren't made in WWF.
Hogan
Hulk Hogan was signed in part to damage the AWA, and some argue NJPW, though WWF and NJPW had a somewhat working relationship at the time. Hogan was AWA's top draw, and WWF signing him away was a hard blow. In addition, Hogan came to WWF at a very different time, when Vince was actively seeking someone that wasn't one of his father's banner carriers to carry the company in a new direction and who had the mainstream entertainment appeal that Vince wanted to integrate into his product. Also, Hogan had the look that Vince likes, perhaps the only look that Vince likes, and is the prototype for the only character Vince really knows how to book.
Savage
Randy Savage was, in my eyes, the CM Punk of his time, in more ways than one. You never get the impression that Savage was ever really intended to be in the spot he ended up taking, but something along the line changed, and he ended up earning Vince's support. Further, even when Savage was champion and being booked as a top guy, with Hogan (and later Warrior) around, you always knew who the "real" champion was. Of the four NJPW talents, Nakamura is the most obvious comparison to Savage, both in work and in charisma, but outside of the dead end Anderson and Gallows will probably occupy, I have the least hope for Nakamura due to WWE's well-documented history of being unable to figure out how to book Asian talent.
Ted diBiase Roddy Piper Steve Austin Mick Foley Jake Roberts Chris Jericho Paul Orndorff Eddie Guerrero
I mean, I can keep going on and on through various era's of the company to debunk this thought.
No, you can't. Your list is three guys from the Attitude Era and then a whole lot of talent from the 80s and 90s. In fact, I'd be generous and go ahead and add Benoit, Ric Flair and Curt Henning in their first runs, and the Legion of Doom to your list, and you would still have a hard time adding someone to your list that wasn't someone Vince signed in the 80s when he was forming the company and trying to establish his brand. Vince bought his biggest competition and still managed to fuck up the booking on the one sure-fire angle wrestling had ever seen. He brought in Dallas Page, a guy who was a legitimate draw in WCW, just to give Undertaker someone to shit on. He fed half the WCW roster to Austin and his son-in-law, and did the same when he bought ECW.
A lot of the guys you mention are lucky to have earned an upper mid-card career. Four of the guys on your list were never the world champion. In fact, Orndorff was never a champion of any sort in WWE. Nakamura is the #3 guy in NJPW. What do you think is going to happen the first time (and every other time) he steps into the ring with Roman Reigns?
All those guys essentially kept the same shit they did other places as far as gimmicks and in ring work.
The "Ringmaster" kept his gimmick? Mankind kept his gimmick? diBiase and Savage, they kept their gimmicks?
WWE buries guys that don't get with their program, not because of where they are from. Damn near every star in WWF history came from someplace else. They hire stars from other places because THEY ARE STARS IN OTHER PLACES.
You're delusional if you think Vince has never signed anyone just to bury them. I would be willing to wager one of Vince's internal monologue selling points for buying WCW was the realization he'd get to fire Jeff Jarrett on live TV.