Uhm... I really wish I could explain this, but sadly I'm not a linguist, just a regular idiot who happen to speak swedish....
So I asked AI for help with the explanation.
The sentence "Jag håller med att bra service är viktigt" is actually a bit tricky, but I'm here to help you untangle it!
In Swedish, "håller med" is a phrase that typically means "to agree with" or "to support". However, when you use it before an infinitive verb (like "att"), it can be a bit confusing.
The correct sentence "Jag håller med om att det är viktigt" is saying "I agree that it's important", where "om" is a subordinating conjunction that introduces the clause. This sentence makes sense because you're expressing your agreement with the statement "det är viktigt" (it's important).
On the other hand, the incorrect sentence "Jag håller med att bra service är viktigt" is trying to use "håller med" in a different way. The phrase "att bra service är viktigt" is already a complete sentence, and using "håller med" before it doesn't make sense. It's like saying "I agree that that's important that good service is important", which doesn't quite work.
In everyday language, you wouldn't typically say this exact sentence to your friends before going to a restaurant. However, you might say something like "Jag håller med om att bra service är super viktigt när man åker ut på restaurang" (I agree that good service is super important when you're going out to eat), which uses the correct phrase and makes more sense in context!
So, it's not exactly "book language", but rather a misunderstanding of how to use the phrase "håller med". Don't worry, it's an easy mistake to make!
I'm not sure I agree with the bot, though, in that "Jag håller med om att det är viktigt med bra service" is something I could say. Maybe not before going to a restaurant with friends, but in an online dating scenario or something, where you're getting to know a stranger and learning about their likes and dislikes.