Re: Mental Powers
I think, perhaps, a lot of this comes down to the fear many have of mental-based characters already being too powerful. Perhaps in some part CoM was created to combat that, I don't know. But I was reminded, reading the last few posts, how opinion is highly divided as to whether mentalists are over- or under-powered or somewhere inbetween. I tend to think they're fine.
Although I don't think CoM makes a real dent either way if the optional rule is used to allow for -3 ECV rolls. Actually, I kind of think things are worse, balance-wise, if GMs take the letter of the law re CoM in 5th, because then there's no SFX mitigation for different minds and I think it's a little too effective, although not by much, perhaps not even significant. And I'm not really blaming the rulebook if GMs don't take SFX into account, but then again I do think that 5ER, as it stands, is too leading with CoM as written.
To the point you made about abuses for PCs, I don't know how bad it is as to be fair the CoM rules state - in what I find to be a bit arbitrary - that "all player characters...are affected as if they belong to the Human class..." - which most GMs are going to end up applying to at least many NPCs to balance, though the text doesn't state that. Clauses like this make the whole thing fudgey, though.