Whether or not its worth it depends on how much experience you have with iPhone repairs. Remember that iPhone 6 has Touch Id home button that is married to the logic board, meaning that if you were to order a fully assembled lcd with a button and just install it as it came - you will forever lose the Touch Id function. Although if you aren't comfortable changing lcd shield and the front camera, proximity, ambient light sensor flex and installing the earpiece, it may be worth it to order the full assembly and switch the iPhone 6's home button. Personally, it wouldn't be worth a penny to me nowadays but on my first and second iPhone screen repair it might have!
Yeah very well could be the glass, some of the cheaper lenses don't allow proper light detection. If you replaced the front flex I'm sure you would have made sure that the sensor is correctly situated.