All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
One of the greatest ways leading to misguidance for some Muslims is to believe in a certain belief, or say a statement, or do an action –as a way of religiousness – and then start looking for evidence proving it.
Rather, the right course is to seek the proof and then act according to it. What some Sufis call “presence (attendance)”, which is the belief that the Prophet attends their circles, is an example of this misguidance. This is why they exaggerate in providing inference for this matter, like what you mentioned in the question.
The texts of the Quran and Sunnah should be understood on the basis of what the first and best generations understood them, especially the companions of the Prophet who were the most knowledgeable of the people, the most sincere, and they were far away from following their desires and from division and disunity.
Ash-Shaafi'i eloquently spoke as he said in his book Ar-Risaalah:
"They [Companions] surpass us in every knowledge, mind (reason), religious practice and virtue, and in any means though which can obtain knowledge or attain guidance; their view is better for us (to follow) than our own view." [End of quote]
So, let these people [Sufis] bring for us a statement from the best generation that has the same meaning as they are saying, or provided evidence proving this meaning which they believe in, whether it is this evidence or other pieces of evidence. This is what judges between us and them.
Otherwise, let us just follow what the first generations have followed. Abdullah bin Mas’ood said:
"Whoever wants to follow a path, let him follow the path of one who has died, for the living are not safe from fitnah (affliction). I mean the Companions of Muhammad . They were the best of this Ummah: the purest in heart, the deepest in knowledge and the farthest from exaggeration. Allah chose them to accompany His Prophet and to establish His religion. So recognize their status and follow into their footsteps and adhere as much as you can to their guidance, for they followed true guidance."
It is not necessary that the word Shaahid (present) used in the Duaa’ uttered during the funeral prayer would have the same meaning when used in another situation.
The following are the statements of the scholars of Tafseer about the meaning of Shahaadah in the verse of Al-Ahzab that you referred to.
Al-Qurtubi said in his Tafseer:
"Allah Says (what means): {O Prophet, indeed We have sent you as a witness.} [Quran 33:45] Qutaadah said: [it means a witness] on your nation, by conveying (the message). Another view said that it means being a witness over their acts of obedience and acts of disobedience. Another view reads: 'Clarifying to them that with which We have sent you.' Yet another view says: 'A witness over them on the Day of Judgment. He is a witness over their deeds today, and will be a witness over them on the Day of Resurrection. We have already explained in Surah An-Nisaa’ [Quran 4], the statement of Sa’eed ibn Jubayr about this meaning.'" [End of quote]
If the Prophet attends after his death, then he would have attended to his companions at the times they were most in need for his presence amongst them, as tribulations took place in the battles of Al-Jamal and As-Siffeen.
Also, if he were to attend, then he would have clarified this to the nation and informed them, and they [the companions] would have clarified this and conveyed it to the nation. However, they knew that he died and moved to the Supreme Companion; Allah Says (what means): {Indeed, you are to die, and indeed, they are to die.} [Quran 39:30]
Perhaps the best evidence that refutes the statement that the Prophet attends after his death is the Hadeeth reported by Al-Bukhaari and Muslim from Ibn 'Abbaas in which he said:
"Lo! Some men from my followers will be brought and then (the angels) will drive them to the left side (Hell-Fire). I will say. 'O my Lord! (They are) my followers!' Then a reply will come, 'You do not know what they did after you.' I will say as the pious slave (the Prophet Jesus) said (which means): And I was a witness over them while I dwelt amongst them. When You took me up. You were the Watcher over them and You are a Witness to all things.' [Quran 5.117] Then it will be said, "These people have continued to contradict your guidance since you left them."
Also, the Hadeeth narrated by Ibn Maajah on the authority of Abu Ad-Dardaa’ that the Prophet said: “I am leaving you upon something that is like a white, bright, and clear path; the night and day of which are the same.”
Allah knows best.