The 3.5 has indeed had some issues during its evolution, but third generation is pretty darn bullet proof.
That being said, things happen - we had a Mercedes Sprinter van purchased new and meticulously cared for diesel that whole engine failure at 25k miles. Luckily Mercedes did a full engine replacement, never heard cause but again - defects do occur in these amazing power plants we see in use…
I totally agree!
Years ago, my new Pontiac Grand Prix developed an engine peep at 50 miles. My Cadillac Fleetwood Diesel needed a new motor after 5000 miles, my Ford F-150 pickup developed a bad tranny after 2000 miles, My Lincoln Mark VIII lost all suspension after 500 miles. They were all purchased new. I can keep going

95% of my new and used, 1–3-year-old cars and trucks have been perfect or near perfect. My '25 Platinum has an adaptive cruise control issue and passenger retractable running board knock, that will need service.
My point is every vehicle manufacturer has some lemon vehicles or at least vehicle issues. That's one reason why many people choose to buy a used low mileage model. Most of the time all the headache malfunctions are repairs. And if 1 year old with 12,000 miles, it gets a longer warranty, (Still 3 years 36,000 mile and 7-year 100,000-miles powertrain warranty with 6 years left), compared to 5-year 60,000-miles powertrain.