First off, I am and always have been a huge Waltman mark, from the Lightning Kid days on, so I won't even try to hide my bias.
I'm not going to pretend that this was because of Waltman, but right around the time he left WCW and reappeared for WWF, Raw overtook Nitro in ratings for the first time in months. When X Pac showed up, the the DX stuff got really hot and the feud between DX and the Nation heated up which more or less launched The Rock into the main event scene. Again not saying all or any of the credit goes to Waltman, he was just a midcard guy but he was great at what he did in the late 90's, and they can't all be main eventers, especially at his size at that time in the business.
I don't see what relevance him never winning the IC title has, the IC title still meant something up until about 2000 and even then, he was a cruiserweight essentially and the Attitude era was not wrasslin as we know it today where a guy Bryan or Punk's size is competing at the top of the card. His feud with D'Lo Brown over the Euro title showcased some excellent matches and in '97 up until Shane "retired" it in 99, I'd say the Euro title held about as much prestige as the IC title does today. Don't believe me, here are your first 5 European title reigns, British Bulldog, HBK, HHH, Owen Hart and HHH again.
You can argue that his relationship with The Kliq definitely furthered his career and gave him more slack for his shady antics when he was a drug addict but he broke into the business on his own merits period. He didn't go on Tough Enough or send his headshots to the office like some of the jabrons have the luxury of doing today and he didn't even know HBK or Scott Hall before his tryout. He paid his dues since he was 9 years old putting rings together and training non stop, something that is missing in a lot of today's reality tv tools posing as "superstars". He was busting his ass on the indy's before breaking in with Global and getting a wwf tryout. If you think he is mediocre in the ring you are kidding yourself or you think Hulk had a stellar leg drop. Watch any of his matches from Japan, his match with Hakushi from SummerSlam '95 or any matches with the Hart's. In WCW his matches with any of the cruiserweights we're always great, his feud with Malenko, Jericho, Guerrero.. I could go on and on about his work in WCW. There's a reason a 6 foot 170 pound stick boy got a deal with WWF and graduated from the rank of jobber, because he respected the business and worked his ass off to hone his craft and was one of the best in ring workers of the 90's, anyone he got in the ring with would tell you that. Along with HBk and the Hart's he helped pave the way for smaller competitors to get any respect from the WWF/E brass.
I will agree his X Pac gimmick got incredibly stale in the end of his 2nd WWE run and his career fizzled. It could have been the booking, lazy writing, complacency on his part or it could have been the meth... that's neither here nor there, his early career speaks for itself.
As for Bischoff firing him, as already stated that was nothing more than a power play to get Hall and Nash in line. It wasn't really a huge deal just showed what a petty douche Bischoff was. Bischoff was gifted a perfect storm of pro wrestling gold, Ted Turner's check book, Sullivan's and his incredible understanding of how to ge heat doing the booking, WWF in a dark period due to courtroom issues and the biggest stars and the hottest angle up to that point in wrestling. He lucked into this scenario not to mention lied his way into the company so it's not like Bischoff was some brilliant pro wrestling mind, let's not forget he fired Steve Austin via phone call a few years prior to this.