i wouldnt say it is a must
it just turn A2 multishot, Musketeer covering fire and Snipe into AOE
but
Snipe is pretty small hitbox, Covering fire have a larger hitbox, but still not as big as those AOE class
you will feel the pain when solo grinding no matter you have or have not Falconer, 30s CD is not going to change much
in grind party either ppl will not take you no matter you have or have not circling, or they will take you no matter you have or have not circling
as for Scout 1, it give very good skill for clearing map as you cant do anything against magic mob, even full cloth, they still hit like a truck
i have a very unusual musketeer, i go wugushi 2>falconer>musketeer
it is very difficult to use circling + snipe alone
but when it come to party grind, any SR/cannoneer/ele will kill the group before my stupid slow react AI falcon start the job
so i wouldnt say falconer is a must, it help AOE a bit if you are going QS3 route, but there will always alternative way to build a musketeer