Experiences may vary :/ Had plenty of S-ranks and world FATEs throughout the years where I'd show up just late enough to not get full credit and some where I was able to even solo. Last Ixion I made it to, was solo as rdm and got gold for a 5-6 minute fight. For larger servers, unless you're an active hunter you most likely won't get wind of an A or S rank until it's already been pulled anyway