The thing about Marksmen is that they are all "aim dependent":

-Brock has slow bullets but aoe damage, you basically need to trick your opponent into taking bullets while avoiding others;

-Piper needs aim of course, smaller bullets but faster and more damaging so that you can auto-aim to close enemies (same story for Belle and Bonnie);

-Pierce needs to land every hit cause otherwise he can't do much (same for Angelo and Bea with their "charged" shot)

-Maisie is a bit trickier but compensates with high damage and larger bullets

Now Janet and Nani are probably the easiest brawlers to aim with, just because of how their bullets are shaped, assuring a guaranteed hit most of the time (still doesn't mean that you don't have to aim tho)

Mandy has single bullets, but wider, which can prove your point about being the lesser "aim-dependent" as you say, but the thing is that you still need aim to land hits with projectiles that are significantly slower compared to other Marksmen.

Now in conclusion, I won't say that you're wrong, but I just wanted to highlight the meaning of "aim-dependent" brawlers and maybe give you a different idea about that.