What the reduction is doing

Notice the shape of it, because it is not a grudging exception tacked on afterwards.

The lightening is in the same surah as the command. It is given for ordinary human reasons: people are ill, people travel, people have work to do. And the instruction that replaces the long standing is recite what is easy, which is a phrase about capacity rather than about minimums.

The same standard turns up elsewhere in four words, with no qualifier attached about how hard you tried. Be mindful of God as much as you can.

None of this makes the night prayer small. It makes it something fitted to a person, in the state that person is actually in. And the classical handbooks do the fitting rather than only saying it ought to be done. Ibn Qudamah writes a graded descent for exactly this reader, in Mukhtasar Minhaj al-Qasidin.

فأما من صعبت عليه الطهارة في الليل، وثقلت عليه الصلاة، فليجلس مستقبل القبلة وليذكر الله تعالة، وليدع مهما قدر. فان لم يجلس فليدع وهو مضطجع، ومن كان له ورد فغلبه النوم وفاته، فليأت به بعد صلاة الضحى.

Our rendering, and it is a rendering rather than a published translation: as for one for whom purification at night is difficult, and the prayer is heavy upon him, let him sit facing the qibla and remember Allah, and supplicate as much as he is able. And if he does not sit, let him supplicate lying down. And whoever has a portion and sleep overcame him so that he missed it, let him do it after the Duha prayer.

Nothing in that treats the descent as a failure, and the last clause hands you a route rather than a debt. The report below is the same instruction on a sound chain: a portion slept through, then recited between Fajr and Zuhr, is written as though it had been recited in the night.