Rude was clearly the best heel WWE had during the late 1980's. Many say Ted DiBiase or Mr. Perfect should have had the belt. I always say, not ahead of Rude.
Why was he so good? Well he was a believable "missing link" from the smaller WWF guys like Perfect, Piper, DiBiase to the monsters like Hogan. He was cut, but not in an excessive way like guys such as Scott Steiner or Trips went for. Rude's body was loved by women and envied by the men.
In the ring, he was a strong, tough worker. Not overly flashy but I don't recall him ever having a "bad match" on PPV for the WWF, even against aging workers like Superfly. His finisher, for its time was vicious and it always burns me today when Ziggler uses it and there is no reference to it's origin... Could they not just call it the Rude Awakening? Oh no cos that then means people ask why he ain't in the HOF!
Rude's real strength tho was in using unique ways to get the crowd to hate him more than anyone in the building. Look back to his feud with Jake Roberts, it was Jake's 2nd major face feud and Rude pulled out all the stops to get him over. He hit on his wife, he put her face on the crotch of his tights... yep read that again, then go and look at it. Of course Jake played his part, but that feud and Jake's success as a face was pretty much owed to their segments and that blow-off match, ironically taking each other out of the World Title tournament!
Rude's best was with the Warrior and it proved he was ready for Hogan. He was able to not only teach Warrior a lot about the ring and how to work but make him look a million bucks while doing so, the loss to Rude actually built Warrior and when he took the title back, even with an assist from Piper it put Rude into the "why is this guy not higher" bracket.
Sadly that's where it started to decline, because Hogan clearly didn't want to lose to "the smaller guy", he didn't see the big picture of the Hogan images on Rude's tights, the heat that Rude would have generated for Hogan by beating him dirty would have prolonged his WWF career for another year at least.
Come Summerslam 90, it was Warrior refusing to job, he'd gotten wind of Hogan's methods and employed them himself. Rude clearly quit out of exasperation, there was nothing more he could do if Vince insisted on pushing those two particular wrestlers.
Ironically Warrior held the title only another 3 months, but of course Hogan was the one who handpicked Slaughter to work with. Rude v Hogan at Mania 7, or Rude v Warrior in the career match would have been a much better feud and match than what occured.
Of course we all know Rude went to WCW and was simply the best heel in the biz for a 2 1/2 year period til his enforced retirement. He did get a World Title there, the NWA/WCW International title. So he held the same belt that Flair, Lou Thesz etc had...
When he returned in 97 as a manager, he immediately made an impact and by 99 was training hard for a return, which I am pretty sure would have seen him win the WWF title as he'd have been a golden opponent for Mick Foley or Austin.
Should he have had the WWF title... Absolutely, should Hogan and Warrior be ashamed for refusing to work with him yes... of course neither will be.