I don’t really understand why you can’t do more structure on your commutes? The roads are either safe enough to commute on, or they’re not. If you’re OK doing 220W, why not do intervals at 250W?
Agree with others that you need some structure. But this can absolutely be done with commuting. I got my FTP to 320W off the back of commuting 15 miles each way to work 4 days a week, plus a long ride at weekends, and 1 indoor trainer ride. I didn’t even have a power meter outdoors, used the indoor rides to calibrate power to HR/RPE. Then looked at the TR plans and adapted them as best I could into my commute. Not ideal as the ride got a lot of interruptions from things like traffic lights, busy spots where it wasn’t safe to go fast, etc. But having some kind of structure is better than no structure at all. And I had great volume - 10 rides and 12-14 hours per week. Can’t bike commute with my current job so nearly all my riding is structured now but FTP isn’t actually that much higher because I struggle to consistently match the volume I was doing back then.