Thats nice but with no evidence this is only your opinion nothing else, please explain why you disagree.
What was the other part, decreasing tanking ability? because that just went in. Or do you mean increasing the supporting/healing direction of paladins?
And regardless of what Wiz had in mind for the exact roles of the three tanks the current problem in regards to raid roles is that warriors are now clearly the king of mitigation (the main tank) as well as the most dps, shadow knights are the king of grabbing agro (and dropping it if they wanted), paladins are the king of....?
The problem is no other class is going to out tank a warrior, out add manage a shadow knight but there are classes that do everything a paladin can do better barring a few encounters where agroing many low resist mobs is needed. And, as I previously said encounters where there are multiple adds at higher tiers a paladin is often useless because of resists.
Now, there are other classes that have the same plight as paladins by which I mean not being the best at a straightforward role such as tanking or dps, specifically noted by Wiz were the monk/ranger. These two classes can tank moderately well, especially adds, and really have little problem with single target agro because of their dps. They both also always add something in general to a raid because of their substantial dps. I am not saying that rangers/monks tank as well as a paladin but they are pretty close, much closer in tanking to a paladin than a paladin is to their dps. In other words (from what I have seen) a monk/ranger/bard can tank adds and probably be around 20% behind in terms of mitigation/avoidance. But a paladin while out tanking these other classes is always dealing 300-400%+ Less dps. And think about this for a minute, the faster something dies the less heals (mana) are needed. So, as long as your ranger/monk/bard are not splatting very quickly they are much more desirable even on fights that involve adds. And if their are no adds why is a paladin even thought to be Needed so badly? Any class can aux tank, might as well pick the one with the most dps, and there are many superior options for group healing than pally ghots.