I feel like you should cover basic rotations for each class.
That's something for a tank-specific guide, as the rotations - and all permutations thereof - can get quite complex. I'm not going to go into details on death strike timing or elusive brew stack maintenance in a broad overview.
I don't love how you describe them as offensive, defensive, personal utility, group utility. Useful description for PVP or character selection screen or fanfic, but it's all just buttons.
The entire game
is "just buttons." What they do, and what kind of thematic package they fit in to, is what defines the classes... and there are definite trends within each class toward specific roles.
Attaching a label that accurately describes what the theme and niche behind the buttons is sort of the purpose of the guide. Warriors really DO have more buttons that affects enemies, Death Knights really don't have spells that work on allies (two: AMZ if you talent for it and Death Coil if you glyph it... and both are pretty much useless, with far better options available). Taking that and using it to give an impression ("DKs are self-focused, Warriors are enemy-focused") is a useful thing for new would-be tanks.
Again, this isn't meant to be an in-depth guide. It's meant to be a brief
summary so people can get a general impression of what a tank will be doing with his or her time. If people want detailed mechanical breakdowns, there are - again - class specific guides around.