Thanks for your email. I actually enjoy writing law firm copy. Other than that, I assure you that I am for the most part sane.
I agree with your assessment of your client's site. It's typical law firm copy that covers the usual bases while utterly failing to engage. It is to your client's credit that they have requested a writer to produce copy that they wouldn't produce on their own.
My experience has been that, the larger the law firm, the more the attorneys seem to obsess on "positioning" themselves as "the professionals." While we certainly don't want to be unprofessional, "the professionals" is no position at all. For one thing, it's redundant: attorneys are professionals by definition. For another, positioning has to do with setting yourself apart. If all law firms are "the professionals," not one of them has a position.
A better approach is to write from the standpoint of what connects with the prospective client. When I recommend my business attorney, I do not say, "He's such a professional. He has great suits, dimples his tie and never speaks with contractions." Here's what I do say: "He's a bulldog. He bites my opponent on the leg and doesn't let go until I get my way." Invariably, the person I'm talking to says, "That's the guy I want," and calls him.
Leg-biting is, of course, over the top for a website. (Or is it?) But if we expect people to read, we must at least engage them, and that means not writing the same old stuff they've seen on other sites. Otherwise, they will only skip-read, if even that.
As I'm sure you know, the more attorneys who have approval/editing power, the weaker the copy will turn out. If the law firm's principals can discipline themselves to (1) limit review to one or two principals only and (2) resist the urge to rewrite and instead provide feedback, they will increase their odds of finishing with compelling copy.