I actually think this is a good idea, though there are some issues with it.

It would allow people to avoid parties like this if it isn't their thing. Frankly, if there is a huge issue of first-timers getting through content because nobody is helping them do it, that's not really a bad thing - it forces SE to take note of the problem. It also creates a reason for people to join a Free Company or linkshell where they can get help for situations like this. There is already too few reasons for people to do things with other people.

The major flaw I see is that not having completed something is not really any indication of how well the person knows their job and knows the battle. There are plenty of people who have cleared things by being dragged through it without having any idea of what is going on. There are also plenty of people who know fights very well from doing it on other characters or from other sources like guides and videos.