as is often the case withという定型表現がありますが

as is often the case with 〜 という表現の 〜 の部分は、名詞が入ります。

この名詞 〜 について、関係代名詞でつなげて、
as is often the case with those who...
という言い方は可能です。次に来る主文の主語は they を使うことができますが、必ずしも they でなければいけないということはありません。

As is often the case with those who try too hard, Harold burned out soon after he realized his efforts were not appreciated at work. And, as is often the case with Harold, he blamed everyone at work for his failure.