Can tenured professors do more about injustice in universities?
There are a lot of things you're asking that are going to fall under opinions, vagaries of the university you're talking about, etc. But here are some concrete things they might be capable of doing:


If there is a faculty union, it is almost certain tenured faculty will have a voice on it. They can use that voice to advocate for any number of causes, including things like better treatment of adjunct faculty, etc. It is, of course, possible for this voice to be ignored.
Similarly, a faculty senate may have some voice in deciding university policy, weighing in on possible candidates for president of the university, etc., and may use this voice to prioritize certain causes.
Tenured faculty will likely sit on faculty hiring and admissions committees. This can allow them to exercise some power in who they hire, and how they are evaluated - for example, are women and minority candidates being given a fair shake? Are we admitting a realistic number of graduate students given the job market?
Similarly, they may serve on tenure promotion committees, curriculum steering committees, etc. and may advocate for teaching performance being a stronger criteria for promotion and tenure, shuffling some classes to better teachers or reclaiming a class from another department that is blowing off their students, etc.


That being said, there is a limited amount any group in the university system can do. For example, fees might be set by the state legislature in the case of a state school, class size is likely more a function of budget than anything else (tenured faculty can't conjure up new FTE positions), and some of these things, to be frank, may not rise to the level of "Something worth protesting over". Additionally, while more protected, the experience of any number of tenured faculty shows that they can be retaliated against.