Suppose for the sake of argument that replacing the whole unit is expensive enough that any part of it failing is effectively the end of the car's life. You could still end up with a more economical car as long as the % reduction in the car's mean time between failures is less than the % reduction in sticker price.

It's kind of like how the most economical car I've ever owned was a rusted out pickup truck that was theoretically on its last legs when I got it. But I only paid $700 for it in the first place, and it lasted me another 3 years with only routine maintenance and wear items needing to be replaced. My 2010 Kia Soul would have to go 26 more years without any major repairs to reach the same price per year of service. (not adjusted for inflation)