School dramas are great for not having a single antagonist! I particularly enjoyed School 2013, Reply 1997, Reply 1994, they are also very light hearted.
There are also some gender-swap dramas like Sungkyunkwan Scandal or Coffee Prince which are very light hearted.
If you are looking for something where the protagonists are up against an organisation the best example I can think of is Doctor Stranger. Angry Mom also has some elements of the bad guys being in an organisation, but there are characters in there which I completely hated. Healer also kind of fits this bill of being up against an organisation but I found it far from light-hearted (it is very good, but quite action-packed).
Sorry to be making all sorts of random suggestions, I tried to take a look at your list to get a feel of the sorts of things you liked but there isn't much on there yet.
