The Sunnah has two elements: Documented ahadith and Traditions passed down, which may or may not get documented through time … It has always been “understood” since the earliest of times that Isa (AS) is alive and shall return as he was when he rose. It is indeed part of the Ahl-us-Sunnah-wal-Jamma’ 'aqeedah in At-Tahawiyya - this was written and documented centuries before the arrival of certain claimants of Isa (AS) - so we cannot be accused of changing our beliefs after the advent of such people. To be honest a clear perspective is written here:
It describes the whole issue you are having with the terminology … There are many references in hadith regarding the “son of Maryam (AS)” will descend - people did not ask if it is the “same” or a different person … they knew who was being talked about …
If a descent is due it sort of demonstrates that an ascent took place in the past … Some scholars namely a certain Pakistani scholar argued that the Qur’an talked about the ascension and the hadith talk about the descension (although there are hints in the Qur’an regarding the descent and hints in hadith regarding ascent) …
At the end of the day if we are serious about this topic we will realise that picking holes can be done on both sides - it is one of those wisdoms - how can 40 imposters come and how can the age of Dajjal be one of confusion and deception if certain accounts of future events are direct, unambiguous … it is part of the Divine Wisdom that there will be controversy in this matter … the clue to finding the truth is to stick to the main body … the same goes for the sects formed from other differences as well as this one … To me it makes more sense in my way of understanding … We can for sure create a chart of concepts and tick off the possible understandings, but I believe the one that will result in the most coherent cross-networked consistent understanding is the one that the main body of Muslims is already on …