[YuriTokoro]

Originally Posted by KyleGoetz

Yuri, hello!

Question about that. Is it because the もっと is sort of emphasizing the cuteness, and it sounds weird to use this emphasis without having already talked about dogs being cute?

Hi, KyleGoetz.

Yes.
もっと is sort of emphasizing the cuteness in student95’s sentence.
When you say “A はBより　もっと おもしろいです”, you need a premise that “Aはおもしろいです”.

Like, you would only use 〜よりもっと【形容詞】 if it were OK to also say 〜はもっと?

As in
欧州史はおもしろいです。しかし、米国史はもっとおも しろいです。
so
欧州史はおもしろいです。しかし、米国史は欧州史より もっとおもしろいです。
??

Both of these sentences are good.
Of course, you also say “欧州史はおもしろいです。しかし、米国史は欧州史よ りおもしろいです”.
However, “欧州史はおもしろいです。しかし、米国史は欧州史よ りもっとおもしろいです。” shows your passion for米国史.

However, just coming out and saying at the beginning of a conversation 米国史は欧州史よりもっとおもしろいです would sound weird and wrong, right?

Thanks.

It’s not wrong. Listeners would understand what you mean, but it just sounds a bit sudden.
If you share a premise that欧州史はおもしろいamong you and listeners, you can start with米国史は欧州史よりもっとおもしろいです.

When you say “cats are much cuter than dogs”, some listeners would think both animals are not cute, so you need to say your premise first.

Anyway, よりもっとis relatively casual.
If you are a professor at an esteemed university and you prefer米国史 very much, maybe you would say;
欧州史はおもしろいです。しかし、米国史は欧州史より 格段におもしろいです
I mean, there are too many expressions.
Good luck!