You don't say if you have the AWD or FWD version nor if you have the 17" or 18" tires. If you are talking about the 18" variant, OEM should have been either Goodyear RS-A or Michelin MXV4 S8.
Speaking of wear, we have 235k on our RX330 AWD with 235/55/18 tires and have never got more than 38,000 miles on a set. I have tried multiple brands (Michelin, Goodyear, Bridgestone) and different models with very little difference. The Goodyear Assurance Comfortred lasted the longest at around 38,000 miles and the OEM Michelin's the least at 28,000 miles.
The only saving grace, I get a nice credit because the tires never come near the tire rated warranty. For the record, I have never heard of what the tire salesperson was telling you about the fact that the warranty doesn't apply. In my experience, at least with Discount Tire, I have them rotate every 5k and as long as they are wearing evenly, they have never second guessed applying the credit.

 

I bought a 2008 RX350, FWD last October (2017) which had almost new Bridgestone Alenza tires (18"). My wife drives it mostly and hadn't said anything, but I noticed a roaring from the rear end at low and high speeds. I took it to my tire dealer and they found the rear tires were cupped really bad. I was told those tires did not 'wear' well on the RX, but the cupping which will cause a bump and noise from the rear was caused by bad rear struts. I had new tires put on and aligned and about four weeks later had rear struts replaced. It now is smooth, quiet, and handles much better. I was told the OEM struts on the RX sometimes wear out around 100k miles. We currently have 117K on the odometer. Point being, you might take a look at the rear struts as the culprit of the bumping and tire wear.

 

were the tires ever rotated?

 

IF A VEHICLE IS MISALIGNED, it will eat on tires.
If tires were not rotated routinely, it will facilitate tire wear.
Hence, it needs to be investigated, how is alignment and if tires were rotated.
That said, I replaced tires on DW RX at around 50 000 miles. Our then 99 RX300 showed no signs of premature tire wear, but I rotated them at least once year. Those cars have major negative camber in the rear, due to independent suspension, so rotation becomes mandatory, or it will eat them on the inside in short time.

 

Oh, and any tire warranty is always mileage prorated up to certain mileage, then you are on your own.

 

my michelins went 62000

 

• Currently at 68k miles on a set of Bridgestone Dueler H/L 422 Ecopia tires purchased almost 4 years ago
• The warranty ended at 65k miles
• Tread depth currently at 4.5 - 5/32, with the original tread depth listed at 10/32nds
• 235/55R18
• 2008 RX350 AWD
• Rotated at each oil change
• Nothing but praise for this set of tires

 

Michelin Latitude Tour in my wife's RX350. Love the quietness/ride quality. Seems to be quiet durable too. I buy nothing else but Michelin.

 

most Michelins balance well

 

Have had no issues with Michelin on my previous Avalon (Primcacy MXV4) and my wife's RX. Now 17 ES350 has Michelin as well and these are some quiet tire.