What do you use to clean the glass? Do you run the car through a carwash? You say you have the defogger on, do you leave that on all the time in the rain? I would stop doing that. Have you tried polishing the glass with a machine polisher and a glass polish?
First thing you have to come to terms with, is its just a windshield and a car. Nothing magic about the glass in the Lexus, its made by a glass manufacturer that makes glass for MANY carmakers. This is not a fault in the vehicle, or the glass, its something that is on the glass and what we need to do is figure out some way to get it off the glass. So, I would just stop taking it to the dealer...stop thinking about lawsuits and lemon laws...there's nothing they can do to help you really...and what they've already done likely wasn't neccisary. My guess is that whatever carwash you use deposits something on the glass and thats whats causing your smearing. In any event, we need to get your glass polished and cleaned.
If you want to try something you can do yourself, I would go to the grocery store and buy some "Bon-Ami" cleaner. Its a powdered cleanser. Make a paste with it, and polish it into the windshield really well with a terry type towel (don't let it run onto the paint). Do that a couple times, then clean the windshield and wipers with a automotive glass cleaner (not Windex), I would use something like Stoner's Invisible Glass), and see if that solves your problem. 99% sure it will. Then over time if it comes back you need to find out how its getting on there. If it doesn't, you'll have to likely take it to a detailer or an independent glass shop and let them machine polish the glass.
I have never had a new car, or a new windshield on a car, that didn't need to be cleaned and polished with something aggressive in order to not smear when using the wipers. That includes all brands of vehicles. The worst was our new Jeep. It was almost undrivable in the rain until I went over the windows really well with the glass polish. Now its great. If the vehicle sits outside and isn't parked under cover, it'll have to be redone periodically over time.