Why Legend of Anle is doing fine with the revenge plot:

I want to start out by saying I enjoy the show in a "this is okay" kind of way but I think the story suffers.

The best way I can describe it is - a really good story is where characters makes things happen. A bad story is where things happen to the characters.

And I feel like too often this show falls into category two. We're 21 episodes in and she's made ~3 things happen. She inserted herself into the crown princess competition. She helped convict the Gu family in the exam cheating scandal. She sent her right-hand (wo)man to go capture the Gu family son to convict the father.

The male lead made one thing happen. His right-hand man was a spy, he figured it out and set up a scenario to offer that spy an out.

When it comes to a fictional story that's not a character study... I think you want something more consequential by episode 21 in my opinion. You want more decisions from Han Ye and Anle whether they are working in opposite directions or not and you want them to be setting up the second half of the show. 

I actually think this is 90%+ a character driven story.

DZY is driven by her desire for justice and to clear her family and their army's name. But, she doesn't know everything about what happened back then (because she was 8). So, she:

• builds an army, builds a navy
• builds an information network
• has LMX build her a faction in court
• engineers a meeting with Han Ye and uses him to enter the court
• first targets Gu Yunnian, who carried out her family's massacre. She plants evidence in the exam cheating case and causes the official to ring the Qinglong bell (which not even the emperor can safely ignore), resulting in the Gu family son's conviction
• manipulates events so that Han Ye goes to Jiangnan and she can accompany him to find the Di family army survivor
• convinces the emperor to bring DCE to court so she can use her for cover
• spreads misleading wanted posters of the Di family army survivor to bring him to the capitol, where she can use him to clear her family's name

Han Ye is driven by: (1) his devotion to DZY and (2) his love for his people and his country, which leads him to (3) wanting to cleanse the court of corruption.

• he meets Anle because he's trying to gain merits to exchange for DZY's release from Mount Dai
• he knows Anle isn't really interested in him and is just using him as an excuse, but he sees her talent and believes that she will be a great minister/official who would bring prosperity to his country and help him cleanse the court
• he knows Gu Yunnian is corrupt but is protected by the emperor. So, he uses a "neutral" outsider (Anle) to help him break Gu Yunnian's power and circumvent the protection the emperor provides him
• he sees she did a great job and is even more convinced she can be a pillar of the country. He brings her with him to Jiangnan so she can win merits and get promoted
• he knows she's good enough at martial arts that he should feel safe when she's with him, and he also knows the spy in his guards doesn't know how good his own martial arts are. He draws out the spy and defeats him, essentially using her as both his cover (showing he hasn't gone without any protection at all, which would be suspicious) and his fail-safe (if by chance he's outmatched, Anle would protect him)
• back at the palace, he again works on getting his father to release DZY, resulting in Anle's using this as an excuse to bring DCE back from Mount Dai
• after DCE leaves Mount Dai, his main goal is now to protect her from the machinations of the court, since he wasn't able to do that as a child

LMX appears to be driven by: (1) his devotion to DZY and (2) his loyalty to the Di family, resulting in (3) his contempt for the Han emperor and plans to rebel/get revenge

• he replaces DZY with DCE, which allows DZY to grow up to be Anle
• he builds a faction in court and an information network to rebel against the emperor
• he cooperates with DZY and reminds her constantly not to get distracted from revenge
• he plots to bring DCE back to the capitol to distract people from DZY

There's more...but that's all I can think of off the top of my head without spoiling too much. But you can see that many of the things that happen are completely consistent with things these characters are trying to accomplish.

SoundofStars, apologies! My response was in reference to Knavery's post above yours :)