The true ZF failures mostly have been happening on the 2016 - early 2017 units (like my MDX that I get back today with a replaced ZF9). Late 2017-2018+ is either too early to tell or they fixed it finally (the latter is my guess, since there were hardware changes in the 2019+ units). The OP's case definitely sounds like some tech didn't put back the right fluid amount (grinding gears is pretty indicative of that).
If you are concerned about the reliability of the 3rd gen MDX then the absolute LAST thing you should do is buy a brand new completely redesigned 4th gen that is new from the ground up. Yes it may share engine and transmission with the RDX and some Honda vehicles, but those have been having their own set of problems (read the RDX forums).
First 2 years of a new redesign regardless of brand (excluding maybe Kia, Genesis or Hyundai) is bound to experience higher rate of issues than the 7th year of an existing model.