I completely agree with both of you. She can't be disabled like that and still have the jobs she's had. She clearly has enough intellect to be able to a.)deliver packages (Feeling Pinkie Keen) b.) have fashion sense(Green Is Not Your Color) c.) Be trusted year after year with getting the southern birds (Winter Wrap-up)Having been a bit of a f*&k-up before I can relate with that scenario. She's likely very eager to prove herself however finds herself overwhelmed by the situations she gets herself into. That being the case, I imagine she is also a very hard worker, just not the most skilled worker.
In every scene where Bon Bon ever speaks, she comes across as kind of a b#tch. In both Call of The Cutie and Green Is Not Your Color she acts very rudely. In The Ticket Master she(like many other ponies, including Derpy) act kind of stalker-ish with Twilight, which she did again in Green is Not Your Color when Fluttershy's disguise fell apart. Lyra on the other hand was the first to cry when a parasprite ate her piece of pie, Bon Bon was simply shocked that it had happened. I am of the opinion that Lyra is likely the kinder and gentler pony of the two. We all know of Twilight's inclination towards being anti-social, however that didn't stop Lyra from waving to Twilight in a warm and friendly manner when Twilight ran by her. So I am sorry to disagree, but I think the reality regarding Lyra is quite the opposite of what you assert.