Why did Samsung skip Ambient light sensor on Samsung Galaxy On NXT ? The phone does not have any automatic brightness control. That's why the battery comes empty so fast. So Samsung must include the sensor on their next edition of Galaxy On NXT.
Yes unfortunately it hasn't been added to the phone, see more here - https://www.google.co.uk/amp/www.androidbeat.com/2016/10/samsung-galaxy-on-nxt-faq/amp/
Hopefully, as you say, Samsung include it in the next version.