That is an excellent question! A question only YOU can answer since after all, this whole comparison thing started off with you comparing an IS350 with a Volvo S80, cars from two different segments. It's funny that you exclude the IS200T but not the IS350 as the IS200T would sort of be an acceptable comparison to an S80. IS200T is more fair only because it's a turbo 2L vs the IS350 being a 3.5L V6 but otherwise, the vehicles aren't comparable as you've pointed out. IS200T/IS350 are actually compact sedans vs the S80 which is a midsize car.
The correct comparison is an ES350 vs a Volvo S80. Even if you upgraded to the Hybrid ES300h, it's still several thousand dollars less in the MSRP. The starting MSRP on the Volvo S80 is $43K while the starting MSRP on the ES350 is $37K and $41K for the ES300h.
No. Cars that are high maintenance are cars that aren't built very well and consequently are expensive to own. Older cars are more expensive to own than newer cars. Older cars are significantly higher maintenance than newer cars. A Prius is the lowest maintenance/least expensive car to own in its segment because it has no belts, no transmission fluid replacements (that it really needs in 10 years), no clutches, regenerative braking, easy on oil, inexpensive tires, and high reliability. Prius doesn't have a lot of parts that are known to fail. I mean, is it a repair or maintenance if you know you're going to have to replace a part on a regular basis? It's like the BMW throttle body problem that trident pointed out. Is that a repair or maintenance? Either way, very expensive and stupid.
I ignored engine size because that's largely irrelevant, I tried to pick luxury cars of a similar size. Should we be including all 2.0L turbo engine cars? Absolutely not. However, the ES3560 vs S80 may be a better comparison, which puts the Lexus at around $5k/cheaper over the first 5 years to own. When we look at the 5-year TCO spectrum that puts us at (I re-did some of these to more appropriately match for size):
Lexus ES350 - $39k, 100% vs best
Acura TLX - $42k, 108%
Volvo S80 - $44k, 113%
Audi A6 - $52-67k, 133-172%
Mercedes E350 - $62-65k, 160-167%
BMW 5s-Series - $56-79k, 144-202%
I believe this still proves my original point that Acura and Volvo are some of the cheapest luxury cars to own. Is Lexus potentially the cheapest? Absolutely. Is it head and shoulders better? Not in the context of luxury cars.
As to your second paragraph... I think you just disagree with the definitions of maintenance and repairs, and are (again) mixing up maintenance and repair costs with TCO. Used vehicle TCO is a tricky game, and can vary a lot from car to car. There's not a lot of solid data out there, but I would posit that depreciation, which dominates early-year TCO, drops off very rapidly because the vehicle value bottoms out, and that repair/maintenance costs would not rise enough to make the vehicle more expensive to own. It may feel worse because money is going into repairs, but at the end of the day one's checkbook doesn't notice the difference.
No idea why you're mentioning a Prius...