I think the difference is those 3UR issues are way easier / cheaper to fix than an engine out issue that the 3.5 TT V6 has.Failure rate isn't any greater that the 2000 100 series transmission, or the 80 series head gasket, or the 3UR cam tower leak, and significantly less than the beloved 200 series radiator. No machine is perfect and the brand value of Toyota reliability is an asset not worth risking on an unaddressed problem. This would literally take Toyota down if it were as big of a problem as discussed. I'd rock a 550 with zero concerns.
New radiator and cam tower fixes are under $3k if paying a dealer…..