Uber / Lyft already have really strong incentives/disincentives to discourage driving for two companies at once. I can't remember the last time my driver had both apps open on separate phones.

Also, a minimum wage per hour is going to probably be much better than driving for both companies in practice, since you'll still be getting paid even if Lyft alone dispatches fewer rides. You're even saving money there since that idle time isn't burning up gas.