So on the 1st gen Moto 360 we can't let screen ON all the time but with ambiant ON which is useless outdoor, but with the 2nd gen is it possible to just use max brightness always ON knowing the battery is better?
" is it possible to just use max brightness always ON...."
I don't think its possible to run Gen-2 under this set of parameters. The Always ON mode dims down regardless of how you set the brightness.
There are custom watch faces that you can download though that are plain vanilla... just dial markers and hands. Dial designs like this will achieve what you are after, plain time-telling with maximum brightness.
IMHO the biggest reason to go with the moto 360 over the other rounders is its auto dimming/brightening function. It works GREAT I have found. It effectively throttles battery usage with dimmer settings indoors, yet runs the screen wide open when its bright and sunny. It effectively prevents accidentally having a dark screen in bright sunlight, while conserving battery with dimmer screens indoors. The major drawback cosmetically is the flat at the bottom. If you are going to manually set brightness or keep it continually cranked up... go with the LG Urbaine or Gwatch R instead.