(Wether or not that disruption has a positive effect for society in the big picture is another debate - but in terms of labor you can't ignore it)
That's certainly the case here in Australia where taxi drivers were making under minimum wage with working conditions that would not be allowed were they employees. It's hard to see Uber as any worse than what existed before.
My understanding is that people got in deep debt to the medallion owner, which they slowly repaid from taxi revenues. Are taxi jobs at the lowest rung that secure and well-paid?
However, Uber (and similar businesses like airbnb) are really little more than the exploitation of legal loopholes to bypass the usual costs of employment law and industry-specific regulations. Socializing expenses is always profitable, and its easy to beat existing players if you aren't paying the same expenses.
Regarding job security, normal employees at least have a collection of legal protections that cover the employer-employee relationship. It's obviously not going to stop every type of abuse, but it's better than nothing. Some jurisdictions have started to catch up and force Uber et al to act properly, but as usual law is (very) slow to update.
Which costs of employment that taxi companies paid is Uber bypassing? Please be specific instead of relying on rumor and propaganda.