They're undercutting public transportation and traditional taxi services that need to operate with a realistic budget that isn't fueled by billions of VC dollars.
If they're undercutting public transport and doing so at a sustainable price, I view that as healthy competition. If they're undercutting solely based on VC subsidies, that will inevitably end. In the Boston market, I think they're likely profitable on an overall basis, just as grocers are overall (very slightly) profitable, even when they sell loss-leaders and give other subsidies to consumers.
Then you have maintenance, wear, healthcare, retirement, etc... Just accounting for fuel and maintenance these drivers are making minimum wage without any benefits, even if they drive full-time.
The so-called gig economy is bullshit that erodes just about everything it touches, from workers rights to public services.