Al-Ghaali refutes this case in his book بالحجة والبرهان لا نسخ في القرآن, pages 152-158. He makes this powerful argument (my brief translation):
Husaam Al-Ghaali wrote:
Muslims, after the revelation of these verses, fought armies more than ten times their number in many places. In the battle of Mu`ta there were only three thousand Muslims against two hundred thousand enemy soldiers. In the battle of Al-Yarmook, it was thirty thousand aganist two hundred thousand. Abu-Bakr then sent them Khaalid ibn Al-Waleed with a reinforcement of nine thousand. One Muslim soldier said, "How many Romans there are and how few Muslims!" Khaalid quickly replied, "How few Romans there are and how many Muslims! Soldiers increase with support and reduce with defeatism, not with numbers."
That is a great argument. If Abu-Bakr, may God have been pleased with him, thought that 8:65 was abrogated, he would not have sent an army to face an enemy more than six times their number, let alone two times. Even after reinforcement, the ratio was still much larger than two times.
I'd humbly add that the flip side was also mentioned by God. He gave the example of the battle of Hunayn,
There Muslims were more than their enemy but they lost. Thus, it is clear from this verse, from 8:15, 8:45, 8:64, 8:65 and 8:66 that God wants to impress upon the believers that numbers are not the issue at all, whether big or small. Why has God repeated this teaching so many times? Because people tend to think that numbers are the most important factor in battle. God assures those who believe in Him that numbers are not what matters in battle, endurance and faith are.
Al-Ghaali sees it the same way and adds a hadeeth of the Prophet (PBUH) saying that the supplication of the righteous and the true is more forceful against the enemy than the weapons of the fighters, and that sins are more decimating of the ranks of Muslims than their enemy's weapons. I could not find this hadeeth. I appreciate it if any reader can reference it for me.
If I recall correctly what I've read about the battles of Badr and Uhud, the battle of Badr had a three-to-one advantage for the polytheists. It is the consensus of scholars that 8:65 was about that battle. When the polytheists were defeated in Badr, they vowed to retaliate with a much bigger army the next time, and they did the following year at the battle of Uhud. According to
Wikipedia, the numbers were 704 Muslims against 3200 polytheists, a ratio of almost 1:5. The Prophet (PBUH) did not try to negotiate or maneuver in any way, he stood fast and ordered his followers to do likewise and defend Medina. If he thought 8:66 abrogated 8:65, he would not have done so. He made a treaty a few years later, at Al-Hudaybiya, so he was not averse to treaties.
Al-Ghaali then details what Abu-Muslim Al-Asfahaani said refuting this claim. Ar-Raazi agrees with him. Al-Asfahaani said (my translation):
Abu-Muslim Al-Asfahaani wrote:
Suppose we interpret this declarative statement (in 8:55) as a command, the command is contingent upon the twenty being able to endure fighting two hundred. The fact that God says in 8:66, "He knew that in you is weakness" proves that the contingency is not there and thus 8:65 does not apply to the situation spoken about in 8:66.
If it is said that the words "Now God has eased upon you" imply that there was a mandate before and it is now eased, we reply that the Arabs used the term easing in the sense of license, not necessarily to imply a reduction of load. Consider,
There, God is giving license to marry bond maidens for those who cannot afford to marry free women. Is that abrogation? No, it's a license at large.
Al-Ghaali finds that a good argument. He adds that 8:66 ends with the words, "And God is with the enduring", thus confirming, rather than abrogating, what He has already said in 8:65.