I don't recall the exact numbers but the spread of the Jd powers "quality" ratings is something like 70 to 230. Sounds like a big spread. But it's per hundred cars. So for the ONE car YOU will buy the difference in "quality" between them is the difference of having perhaps only 0.7 problems in the first year versus having maybe 2.3 problems in the first year. And the "problems" being compared could be anything from the engine blew up to "I don't like the way the radio knob feels and the dealer can't fix it". The JD power numbers are nearly worthless for retail buyers. If, OTOH, lots of Fiat owners are actually finding that the engines are blowing up, that's a different story.
I wouldn't doubt it. Between 1972 and up till a few years ago I drove a lot of gvt fleet cars. There was a major change right around the late 70s where things went from me having a list of things for the shop to fix every time I sent a car in for it's scheduled service to the cars almost never needing anything fixed. It was pretty much across teh board, didn't much matter what make they were buying, GM, MoPar, AMC, Ford. By 1980 the old "here's a list of things to have the shop fix" was a thing of the past. And most of the stuff that did go wrong was really pretty minor, a lock motor would go bad or something like that OR rarely a major issue fixed for free like transmissions in Dodge Diesel 4x4s that couldn't take the torque of the engine. And that kind of stuff isn't going to show up in the JD Powers numbers that get all the airplay.
I'd say look at consumers reports info but it's often crap too but at least it tracks things for real life cars for several years. Unfortunately it suffers the same deficiency, now that everythihg is really quite good stuff that's on the lower end of "quite good" winds up with a black dot as if it's junk. Some of the cars CU rates are good are crap to actually live with and drive whereas some of the "bad" ones are quite nice to live with and drive.
I guess there's no perfect system.