Can ya go look? Check the PSI of the tires too while you're at it.
Consumer Reports have never impressed me with their tire ratings, and different tires react differently on different vehicles. Really what you need to do is get the firsthand experience of people who own your exact car. I've driven Lexus sedans for 13 years and have put well over 300,000 miles on them, 160,000 of those miles in the ES. I'd consider myself a pretty good resource. Believe me when I tell you, the wrong tires will make you think your Lexus rides like a dog. The right set of tires will consistently impress you.
Other than tires it could be worn ball joints...but my ball joints were about ready to come apart on my ES before I had them replaced...and I noticed none of what you are experiencing. Could be a bad motor or tranny mount...but I had a falling apart dogbone mount and experienced none of what you are experiencing. Have you tried having them road force balanced? If the ball joints are fine, the mounts are fine and the road force balancing shows nothing and does nothing...it must be the tires. The gradual declination of the quality could come from the aging of the tires, which was my experience with several other tire brands on the Lexus, including Bridgestone which is the same company as Firestone.
Firestone makes a sh!tty tire, and sh!tty tires are very hard to balance and keep in balance and balance is incredibly important to how a Lexus rides.