Unlike Steins;Gate, the time travel mechanics in Link Click aren't as well fleshed out

The time travel mechanics aren't as fleshed out because we're only in the first season. We don't know anything about Lu Guang and anything about his backstory other than how he met Xiaoshi. Notice how Lu Guang tried to hide the fact that Emma died to CXS? I have a feeling there's a strong reason why he's been so secretive

I've already noticed a few plot holes

Which plot holes do you mean? I noticed a lot of odd things that happened in the show can be explained by another experienced time traveller that's affecting the timeline.

As to Emma's death node being changed, we still have no idea if major nodes actually cannot be changed, or if it's just Lu Guang's false perception that it can't be changed. It's also possible that Emma was going to die regardless, and CXS's meddling just accelerated the timeline