I'm pretty sure Kanan didn't have much frontline experience if any since IMO A New Dawn strongly implies he was newly elevated to Padawan when Order 66 hit. Zeb has military experience but does he have experience training new recruits or in coordinating missions on a large scale? Hera I seriously doubt has any combat experience other then her time fighting the Empire.
If Ahsoka actually gets added to the Ghost crew on a permanent basis yeah that could easily become a bad thing. If she sticks to a mostly off screen command and training role I don't see what's so horrible about it. And the offscreen role is what she has been in so far except for when an emergency called for everything her resistance network could scramble to be deployed.
Complaining about what she's done so far is like claiming that the appearance of Mon Mothma or Admiral Ackbar in Return of the Jedi stole the focus of the story away from Luke, Leia, Lando, Han, Chewie, and the droids.