I actually think that the core problem here (if any) were the jury instructions, not the counsel's closing argument. If the instructions were right, then the trial court's admonition that counsel's arguments aren't the law (and to follow the instructions instead) would have solved the problem. By contrast, if the instructions were wrong, then reversal is probably required anyway -- regardless whether counsel for defendant made an argument based on those instructions during closing.
It's also somewhat weird to have an opinion that esoterically talks about the underlying legal issue that went to trial -- here, whether the risks to the plaintiff firefighters were something other than the inherent dangers of their job -- without any recitation of the actual facts of the case. Those are generally relevant, no? There was a whole trial, after all. Maybe a paragraph or two (or more) about what actually happened that gave rise to the lawsuit would be a nice background -- or introduction -- to the underlying legal issue, rather than a purely esoteric discussion of the doctrine untethered to any actual facts.
But, yeah, I could see how one might find the instructions here confusing (or inaccurate). Potentially, anyway. (Whether the jury was, in fact, likely confused by them would require me to know a lot more about the actual facts of the case and/or evidence at trial than is available here.)
