Ridehailing increases congestion if the city's public transport system is terrible.
This is not a fault of ridehailing, it's a symptom of bad infra.
Most of those gig jobs would start disappearing
There's no job to be "lost." They aren't going to turn you away for a "job" or "fire" you because you literally aren't employed by the company. Think of it as if you are licensing Uber/Lyft software to generate leads for your own business. That is literally how they think about it and what the driver ToS says.
It is sustainable to do that if by sustainable you mean have a profitable long term business that is cash flow positive
It would likely massively hurt share prices because you’re trading growth for profitability
The best way to think of drivers is that they are customers who are licensing Uber/Lyft software for lead generation for their own business. In a recession a seller of lead generation software (Uber/Lyft) is not going to turn customers (drivers) away. It just might not be profitable for you as a customer of lead generation software to buy it if there aren’t leads, but I don’t think anyone knows what will really happen to rideshare demand if the economy tanks. I think it will go down, but it might not go down as much as one might think.
How much profit can Uber make if it cuts 'certain' cities?