Yup, people don't realize it but shamans can tank really well and even get into raids with the proper guild and effort, there's even a whole shaman tank guide about it.
Paladins can tank raids, but its all a matter of how much effort you put into it to make it work.
Mana issues are greatly exaggerated and pushed by people who haven't played since Vanilla 15 years ago.
Not having Taunt is not a big factor if your guild is experienced enough. The same thing goes for threat.
Are paladins tank optimal? no. Are paladins viable? hell yes. I'd argue they're a slight-semi step above viable and bridging onto optimal.