I think all of the ECW wrestlers with the exception of RVD and Dudley Boyz were misused in the WWE.
And among the ECW wrestlers that were misused, I think Tazz was treated the worst. At least Raven was able to set the record for most hardcore title reigns and was able to win matches against guys like William Regal, Goldust, The Big Show, Steve Blackman, Billy Gunn and Bradshaw.
What did Tazz get? The first win over Kurt Angle, ECW World title while under WWE contract, three Hardcore titles that didn't even last a day each (hell, even Spike Dudley got more Hardcore title reigns), a victory over Eddie Guerrero on Sunday Night Heat, a feud with Jerry Lawler and the World Tag Team title. That's it. The other ECW guys all got singles title reigns. Both Spike Dudley and Saturn got the European title. Tazz could've been European Champion in 2001 but he was going through that jobbing phase where he lost like six matches in a row to everyone from Stone Cold Steve Austin (in 43 seconds) to the Big Show to The Undertaker. He also could've been Intercontinental Champion, but the WWE buried him in consecutive hardcore matches. They basically wasted him as a joke jobber, yet he had great mic/promo skills and wrestling skills. If the WWE didn't want him to become the WWE Champion, they could've at least given him a lengthy singles title reign as Hardcore Champion or something.
Dean Malenko = WWE Light Heavyweight Champion for a long time
Eddie Guerrero = WWE Champion, European Champion, Intercontinental Champion
Chris Benoit = World Heavyweight Champion, Intercontinental Champion
Rob Van Dam = WWE Champion, ECW World Champion, Intercontinental Champion
Chris Jericho = WWE Champion, WCW Champion, Intercontinental Champion
Rhyno = U.S. Champion, Hardcore Champion
Lance Storm = Intercontinental Champion, World Tag Team Champion
Saturn = European Champion, Hardcore Champion
Spike Dudley = European Champion, World Tag Team Champion, Hardcore Champion
Jerry Lynn = Light Heavyweight Champion
Raven = Hardcore Champion
Stevie Richards = Hardcore Champion
Mike Awesome = Hardcore Champion
All of these guys got to literally 'touch' a singles WWE title.
Tazz = ECW World Champion, Hardcore Champion, World Tag Team Champion
The only other ECW stars that I can think of that came close to Tazz in equal burial are Justin Credible and maybe Tommy Dreamer. I'm not including any of the originals that came to WWE for the WWE's ECW, because they weren't contracted superstars in the WWE back in 2000-2002.