Downsized from 19" to 17" and somehow... ride quality is worse?

...Unless the side wall is increased by the amount the wheel size is decreased, right?

If wheel diameter + twice sidewall = overall diameter, then the overall wheel diameter can remain the same for a 16, 17, 18 or 19 inch wheel.

That isn't petty, gullible, rude or plutocratic. There is no presumption in explaining an error in your analysis, but I hope you've enjoyed seeing how the other half live.

 

I would like you to consider that your tire choice may have been excellent, but that you aren't used to the aural cues that small, cheap cars deliver. (Yes, the price for a prius isn't low, but in the modern context it's a cheap car.)

I came from VWs that are tuned to ride softly and quietly. When I test drove a current generation Corolla, it sounded horrid and tinny, like someone had stuck wooden wheels on a garbage can. I ordered one, changed the 16 inch wheels for 15 inch wheels, and got used to the terrible, cheap noises.

Toyota builds a reliable and efficient car, but the driving experience feels a decade out of date and cheap. We have a decade old Camry and even that is much nicer.

Could you have a small car owning friend go for a ride with you and get his reaction? It's possible you've done everything right and time will allow your expectations to adjust.

You don't want to play king of the Autobahn on very low pressures because you'll risk a build up of heat and tire failure. If you are always driving under 80mph and just running your tires slightly soft you should be fine. However, your sense that the softer pressures aren't helping makes me think you might not be used to the car's noises yet, so getting through a period of acclimation with full pressure might be worth trying.

I've been looking for the end of this trend for a couple of decades, but it never quite arrives. In my opinion, Toyota ruins Corollas for the cold weather/pot hole climates with 18 inch wheels.

 

Yep, OP probably needed a larger car like Camry that rides and feels more comfortable.