I don't know how you can say Ted DiBiase wasn't maximized. He was the top heel in the company for about two years. He would headline PPVs and the house show circuit with Savage for almost a year.
Back then, you didn't need the title. I remember an interview with DiBiase where he mentioned a conversation he had with Vince. Vince basically asked him, what would give you more heat? Giving you the World title? Or you making up your own title and claiming you're the champion? Ted DiBiase was a smart enough businessman to realize it would be better for his career, better for his character as a heel to create his own belt. It got him more heat. The more heat he had, the more money he made. And that's how the business was different back then. It wasn't about winning the title. It was about making the most money you could.
A lot of people are mentioning guys like Jake Roberts, Mr Perfect, Rob Van Dam, etc. WWE did maximize on these guys. Could they have gone further? Probably. But it wasn't because they weren't given the opportunity. These are guys who screwed themselves with partying, drugs, etc.
I will agree, some guys like Vader and Bam Bam were under utilized. These were big guys who could go. They were the monsters that Vince loves. Apparently, if you watch the shoots they blame it all on the kliq. In hindsight I find it kind of shocking that Vince didn't push them harder.
I always thought John Morrison could have been bigger/better than he was in WWE. But he apparently had his own backstage issues with his girlfriend. And Sean O'Haire. I don't know really what happened to him. But he had the look, the moveset and the body that Vince loves. It's kind of surprising that he just disappeared, but I don't really know his story.
I never saw what was so special about guys like Carlito or Kennedy. Thought they were mostly bland, benefitting from WWE packaging them into something sort of interesting. But even then, not interesting enough to really get over on their own.