Time travel/loop without dumb protagonist

Hmm these are some hard wishes.

These are some well done time travel dramas but that don't fulfil one criteria:
 Mr Queen  - not a very logical ending
 Signal  - open ending
 Moon Lovers: Scarlet Heart Ryeo - not a happy end

And then there is the rest that somewhat fulfils all your wishes of good drama, happy end;
Someday or one day 
Reset
365: Repeat the year
Chicago Typewriter
Tunnel
Nine: Nine Time Travels
Tomorrow with you
Go Back Couple
Relife - kinda/kinda not time travel. Leads become younger but they don't actually go back in time,  I'd actually recommend you to read the webtoon instead of the drama. The webtoon is really well done

Not the typical time travel/loop but such an interesting story in terms of the writing and twist. First several minutes of ep1 kind of dialogues heavy but you will get hooked easily when the time travel/loop starts. The best jdrama this year so far. Not a romance genre though and more realistic protagonist.

https://mydramalist.com/743381-brush-up-life

 dramalistsite:

Time travel/loop protagonist tring to save someone life/prevent something

 dramalistsite:

smart protagonist

 dramalistsite:

happy ending for the main couple

Meets your criteria:

• Lost Love in Times - Switch to an alternate timeline (a bit like a single loop or reset). The FL is trying to prevent something to save many lives. She and the ML are both smart and capable, and they get a happy ending.
• Secret - Time travel. In the end, the ML tries to save a life / prevent something. He meets your criteria for "not dumb" / dazed. It's a movie but otherwise fits.
• The Eternal Love Season 2 - In season 1 the FL's soul time travels. In season 2, the ML time travels and there's sort of a loop aspect. The FL isn't particularly smart and didn't have a mission to prevent anything or save anyone in season 1, but the ML is mostly smart (he's sometimes a bit dumb when it comes to interacting with the FL), he's not phased by the time travel and in season 2 he tries to do a few things, including preventing something / saving someone's life. The main couple get a happy ending.
• The King: Eternal Monarch - Multiple universes with some time travel. Someone (turns out to be the ML) tries to stop a coup and save at least one life. He meets your low criteria for "not dumb" / dazed / dense, but other characters spend a fair amount of time being dazed by the multi-universe / doppleganger situation. I don't really remember the ending but I'm pretty sure it was happy.
• +1 Queen In Hyun's Man - Time travel. The ML is smart, adapts quickly and had something he was trying to do related to political stuff in the past (I'm afraid I forget the details). The main couple gets a happy ending. One caveat: the FL is the main character (even though the ML is the one who does the time travelling) and she isn't all that smart. 

Doesn't really meet most of your criteria, but it's sort of in the ballpark:

• +1 Moon Lovers: Scarlet Heart Ryeo - The FL's soul time travels. Once that happens, the FL sort of tries to prevent something (the ML becoming a king that went down in history as a tyrant), but she doesn't treat it like a personal mission. The FL is from the present and her soul time-travelled to the past and took over the body of a noblewoman. She's not a genius, but I'd call her smart. Her host body ultimately dies in the past (where the ML is) after leaving him, marrying another man and having the ML's child (for reasons), and after all that the FL wakes up in her own body in the present. Not a happy ending for them as a couple, but the FL finds out she succeeded in preventing the ML from becoming a tyrant, and the ML finds out about their kid. So some bittersweetness.
• +1 Mr. Queen - The main character is a man in the present. His soul travels to the past and he wakes up in the body of the Queen (hence the title). He's not a genius, but he's a skilled chef and a resourceful person. He isn't really trying to prevent anything or to save anyone's life, but he does take a bullet for the King. IMO the ending is not a happy one for the main couple, but it's open for interpretation and many people would disagree with me on that one (the writers included probably). In some ways it's similar to Moon Lovers. The main character wakes up in his own body in the present and finds out good news about the King's role in history. The King loses the person he fell in love with, but gets a sort of shadow version of "her", and also rules well as king.
• +1 Splash Splash LOVE - The FL time travels. She's not book smart, but she's smart enough in her own way / not that dazed by the time travel. She doesn't really have a mission to prevent anything or save anyone's life. The ending is open (implied to be happy as Czakhareina noted above).

AH   

I watched lots of your recommended dramas, thanks once again for the detailed reply.

maidenholmes 

"She is a reporter who reports on a murder trial based on whether she likes the personality of the lawyer."

I like this character already :)

Dramas:
Juunen Saki mo Kimi ni Koishite - nice scifi romance
The Warp Effect - this was quite good mystery time-travel drama, but contains lgbt (BL/GL) and sexual content, main couple is straight. If you mind lgbt or sexual content, then don't watch it.

Movies:
Alienoid 1
Returner