The issue has little to do with the number of pixels, it’s the pixel density that presents a problem. Afaik, it is not currently possible to manufacture at the required dot pitch, even at the size of the Watch display. The pixels on the Samsung Wall are huge in comparison.Generally speaking (LCD, OLED) you are right, but for MicroLED it is see opposite. This is also why i.e. Samsung's The Wall consists of multiple smaller panels. As it is too difficult right now to produce many pixels without failure.
That said, I’m sure we’ll see an microLED display in Apple Watch before any other product.