Once again, I never said that X class can't do X role in a grp/raid, I said that certain classes aren't a viable option, some classes don't even have 1 single viable trait line, namely the RK and Guardian, take a look at their class forums and you'll see that's its not only me that is saying this. If your class doens't have any viable trait line it means that you'll be far less likely to be considered into a group/raid. Does this mean that not a single Guardian or RK will see group action? Obviously not, but it's much more difficult to get into a group, especially if you aren't in a great kin.
You'll still be able to do any role in lower tier content and in certain parts of a raid that favours that type of class, but in general Guardians aren't a viable option, just like RK dps. Thus you'll notice that players in their respective class forums aren't exactly thrilled about their current situation.
I also never said that it's captains fault that other classes got far less viable trait lines, however Captain tanking is vastly superior to other tanks in almost every scenario. However that doesn't change the fact that captains are very OP in yellow, would a nerf to Yellow cappy suddenly make other tanks excel? Ofc not, devs should sort out the other tanking classes first before looking at Yellow Cappies.
Personally I also prefer the old school captain, instead SSG will have to balance a whopping 4 tank classes (5 if you count champs) against each other.
I wouldn't mind keeping the actual trait trees, I do however oppose the multi role system like many of the newer MMO's have for lotro.
Lotro unlike those games were never designed from the ground up with that class system in mind.