Is the character of Al-Qa'qa' ibn Amr al-Tamimi real, or was he fabricated by Sayf ibn Umar, who was not his contemporary?

Al-Qa'qa' ibn Amr al-Tamimi was a revered Companion (Sahabi), whose biography can be found in biographical dictionaries such as "Al-Isabah" and "Usd al-Ghabah." Sayf ibn Umar did not invent Al-Qa'qa'; rather, prominent Hadith preservers (Huffaz) like Ibn Abi Hatim, Ibn Abd al-Barr, and Ibn Hajar wrote his biography, mentioning his life and virtues. However, they criticized Sayf's narration regarding Al-Qa'qa's witnessing the death of the Messenger of Allah, peace and blessings be upon him. Ibn Abi Hatim described Sayf as "matruk" (abandoned/unreliable), and Ibn al-Sakan described him as "da'if" (weak). None of the prominent scholars denied the existence of Al-Qa'qa', and it is not known that Sayf claimed to be his contemporary; rather, he narrated his accounts with his chain of transmission (isnad).