I mean, "grossly negligent" and "extremely careless" don't really matter legally if you aren't charging her with anything. Either is a really bad quote. Both are negative connotations. And whether "grossly negligent" or "extremely careless," we're talking about her handling of classified info. We're not charging her, but she's lucky we aren't is the conclusion I take away from either quote. If the FBI was in the pocket for Clinton, they would literally have just said, "no charges" and closed the investigation.
"To their dismay" is some serious editorializing. I'm sure there were some people who were dismayed that the investigation was reopened, just like the FBI agents that leaked stuff to Nunes and Giuliani during the campaign had a bias. It sure didn't help Clinton though! And like with the ongoing Trump campaign investigation, if the FBI was in the tank for Clinton, they literally would have sat on that until after the election.
Since the Russia investigation was ongoing during the campaign, the Liberal FBI was really, really bad at their jobs if they said, "welp, no reason to bring this to light ahead of the election, but we'll REALLY have him if he is elected president and we continue the investigation!"
SB said this better than I, but my read of the IG Report matches up with his "If anything I think that all of this has shown that Comey helped Trump because he thought Clinton was going to win and after her win he didnt want the right wing conspiracy groups to say that the FBI helped Clinton."