This bug has remained unnoticed for over a decade now, mob AI changed ages ago so now whenever you punch a mob it pauses for a second before attacking, I think it has to do with the AI having a probability of attacking so it takes time to calculate, this makes the game easier and less realistic because if something were to attack you in real life, it wouldn't pause after getting hit (maybe if you hit it hard enough on the head to get stunned, but not every time)

back in minecraft beta mobs were much more difficult, and one of the reasons is because there was no pause every time a mob was attacked, this seems like a very big issue with the game that has gone unfixed for over 10 years now and it used to be how it should be

here is a video comparing beta/alpha to modern, at the time 9:10 he shows the difference in mob AI (sorry about the title of the video this is the only video I can find displaying the issue, I'd record it myself but I'm lazy)

https://www.youtube.com/watch?v=4A1w-Y_Wv5U