He had been working all day, so he fell asleep as soon as he got home.
He worked all day, so he passed out as soon as he got home.
ご質問ありがとうございます。
He had been working all dayとHe worked all day、どっちでもいいですよ。ただ、「〜していた」を直訳すると、had been XXingになります(この訳し方は日本の英語教科書に記載しているはずです)。でも、他のネイティブな人と話している時にHe worked all dayは全く同じ意味ですので、気にしなくてもいいですね!
ご参考になれば幸いです。
He worked hard all day, so he fell asleep as soon as he got home.
He had a long hard day at work, so he dozed off not long after he got home.
この場合、kazumasaさんのおっしゃるように表現するのが正しいです。
ーHe worked hard all day, so he fell asleep as soon as he got home.
「彼は1日中働いたので、家に帰るとすぐ眠りに落ちた」
to fall asleep で「寝入る・眠りに落ちる」
as soon as he got home で「彼が家に帰るとすぐ」
ーHe had a long hard day at work, so he dozed off not long after he got home.
「彼は1日一生懸命働いたので、家に帰って程なくうたた寝を始めた」
to doze off で「うたた寝を始める」
not long after he got home で「彼が家に帰って程なく」
ご参考まで!