As with much of the economy, it's winner-take-all. I would put Zenni Optical alongside Luxottica as the duopoly at the moment. Warby is popular, but it's driven a lot by marketing and VC.
I think online eyewear sales and awareness have been spiking over the last 5 years, and they have serious product market fit. You tell anyone about the existence of online eyewear and the price and they are sold. Luxottica is winning based on market ignorance at the moment IMO, it's only a matter of time.
[0] https://www.statista.com/statistics/256664/sales-of-the-lead... [1] https://www.marketwatch.com/press-release/zenni-optical-cele...
The only downside I have with online glasses is you making adjustments to the fitting of the glasses. Your eye doctor will usually do this for you when you buy glasses for them, but online glasses require you to do it yourself or go into a store (if they have one). With that said, still not a big enough negative for me to go back to buying from my eye doctor.