No products made are 100% defect free, but a quality manufacturer stands behind their products as Hyundai did here.
I didn't find a single cosmetic, mechanical, or electrical defect on a 2020 Mazda CX-5 Signature I owned for about a year or a 2019 Mazda MX-5 Miata that I've owned for about two years. Both of these vehicles were designed and manufactured in Japan. I don't recall finding any defects in a 2007 Honda Ridgeline built in Canada. The vehicles with the most problems I've owned were 2017 and 2019 Honda Ridgelines built in Lincoln, Alabama - we're talking more problems than even the Fords and GM's I used to own decades ago. I'm currently in a 2021 Ridgeline that has been much better...so far.
looks like the didn't fix the transmission, just replaced it with a new one. Fixing it would probably take more time and $$ and Hyundai just replacing it should be a good move
Dealers don't open transmissions - regardless of brand. If a transmission fails in warranty, it'll be replaced with a new or remanufactured unit at the automaker's discretion. The failed transmission will be returned to the automaker for a failure analysis then remanufactured, if possible. If a transmission fails out of warranty, they'll either send you to a transmission shop or sublet the job to one. Transmission work at a dealer is limited to replacement, torque converter replacement, dry clutch replacement, and external solenoid or pressure switch replacements. They don't mess with internally-lubricated parts.