Producers come and go but Kenzie and YYJ aren't going anywhere, they may participate on other works but as long as they keep producing music they'll be releasing songs for SM groups, they are the ones who have shaped SM's sound for not just years but decades.
In fact, SM doesn't have that many "in house producers", most of their songs are taken by demos sent by many different ones from all around the world, and although they have some producers they often contact with like Moonshine, Adrian McKinnon, LDN Noise and now DemJointz the amount of producers they have worked with is insane. They even had Darkchild produce NCT 127's Favorite lol.
You can't have too many ideas with writing. Writing's a one man job, a few men sometimes. You can't put 10ish people in a room and say "okay, write lyrics," cause that's not how it works. Same goes for production, you can't have too many ideas.
I do think songs can have added embellishments though. Yoo young Jin did a great job with the rework of Next Level, lyrics and arrangement wise.
I understand this point of view from a writing perspective but I disagree with the production. Songs with many producers with different ideas can make each section of a song amazing, because different producers have different strengths and specialties.
In fact, the mix of genres on a song has been one of K-Pop's trademarks for a long time, because otherwise it would be like listening to an average western radio pop song, which in my opinion completely misses the point and would make the industry much more dull. A song can have 10 producers and if every section is well done, the transitions are clean and the song has a personality to it, I will like it.