Verse 8:66 was revealed a long time after verse 8:65 was.
This is important information. Does he provide any specifics?
No, he just states it. Nearly all narrations about circumstances, timings and order of revelation, nearly all of them are weak in terms of their authenticity.
I looked it up in the exegesis of Ibn Katheer. He doesn't mention the delay, but he mentions something quite relevant to the claim! He quotes Ibn Abbaas saying, "When Muslims are half their enemy, they cannot run away from them, but when they are less than half they
do not have to fight them and it's
permissible for them to avoid them." Ibn Katheer says that Mujaahid, `Ataa', Ikrima, Al-Hasan, Zayd ibn Aslam, Ad-Dhahhaak and others have said likewise.
That proves that there is no abrogation here, since having a choice means the command is not annulled; it is merely an option. To put it another way, if Ibn Abbaas has said that when Muslims are less than half their enemy, they
must not fight them, then he would be making an abrogation claim of 8:65, because only then is the command annulled.