In regards to the main question or topic title.. Onza being a good or bad starter bike, I'd say yes personally.
Why:
They have bikes to cater for people ranging from Beginner to advanced, For example, the Onza RIP or Onza T-Bird are by far the most beginner friendly bikes, and also very affordable.
For more advanced riders there are the Pro Series and Comp series etc, As i saw you mentioned you had a Onza PRO, well i have to say my friend has a 2004 onza PRO and its a really
lovely bike to ride.
Conclusion:
Yes, Onza bikes are definatly a good choice for a beginner, they are reliable and in most cases affordable, Also if you're having that much trouble with your brakes and have no clue
what to do to sort it out, either take it to a family / friend who may know what they're doing, or if not just take it to the local cycle shop, as i'm sure they will be able to help.