You cannot uninstall the new update on your watch. I have been chatting with Apple all morning as I woke up to the 5-day forecast invading my screen. Yeah NO.
While chatting with them, I did figure out if you scroll waaaaay up to the top of the middle complication, you can turn the middle complication off removing everything, so it ALMOST looks like the old modular face, but there is no option to put the watch time there, and there should be. You should be able to pick to put the date and time in any box, top left, top right, middle, bottom left etc. The representative agreed and sent the request to the appropriate parties. I told her nobody in their right mind, wearing a watch to know what time it was, wanted the 5-day weather forecast, UV index, rain or wind as the focal point on the watch lol........