Yeah, I can agree to this when it concerns new players, especially if they've never done a Hamidon raid - adding something that indicates potential strategy concerns to the mission initiation dialog would be a nice warning (as opposed to learning from trial and error). That seems reasonable.
I don't see this warning as needed for the rest of the player base though - if you are fighting Hamidon, even in a weakened state, it needs to be held. That is a pretty well understood strategy that dates back to Issue 0 on legacy, as far as raiding goes. Even for the folks who have never done a Lady Grey Task Force before, odds are they are going to team up with someone who has.