Would the taxi companies that owned all the medallions have allowed this to happen if their existence wasn't threatened? Or would they lobby to stop this at all cost because it doesn't benefit them?

No taxi lobby stopped Uber.

So hundreds are dying due to Uber?

There is a sexual assault every 8 minutes caused by an Uber driver.

Googling says for example Uber has 400 assaults in San Francisco and the taxi industry had 14.

https://www.nytimes.com/2019/01/07/us/uber-driver-murder-trial.html#%3A%7E%3Atext=Former+Uber+Driver+Pleads+Guilty%2CU.S.

I can't find any examples of taxi drivers murdering their passengers. All news is about taxi drivers being murdered by their customers.