Is this really the same as 彼らは騒々しいことおびただしい? It feels totally different to me...

えっ

ちゃう？

It seems to me they're two instances of the same type of construction, which is not to say that i don't think the question deserve its own answers.

*deserves

One subtype of that construction which it occurs me to mention is the one that have 如し as part of the predicate.

Like 動かざること山の如し.

「心清きこと水の如し」 「君子の交わりは淡きこと水の如し」 「危うきこと累卵の如し」 「生を視ること死の如し」なんてのも成句的なものとしてあるみたいですね

彼らは騒々しいことおびただしい, as well as the entry in meikyo 事柄の程度が最高である意を表す。「面白いことこの上にない」「手のかかることこの上にない」 and other predicates mentioned in that linked Q&A (はなはだしい) as well the answer itself all point to the predicate being something which indicates high degree or frequency.

Because of this I think the 全く不愉快極まる sentence seems more to me like just a normal sentence, not an occurrence of this construction.

電車の中などで見る最近の若い者の態度の悪いこと、実におぞましい。電車の中などで見る最近の若い者の態度のいいこと、この上なく心温まる。I do find myself wanting to put in emphasis words for the sentence to sound good though.