I can answer that as following here:
1: Mamluks had 7/6/7 on Tech, I had 9/8/9, so I was far ahead.
2: They had no mercenaries because they had no money and had many loans, they couldn't even hire new troops.
3: He had two very weak generals and I had 2 good generals and one admiral.
4: It was just immediately after I started the war they had somehow 54000 troops out of nowhere, and their allies couldn't even get to us, they bordered rival territory, so they couldn't get access anyway.
5: there were no mountains at all, just plain desert, but there was no - modificator at all.
6: My army maintenence is before I go to a war, always full and their morale was very high, higher than Mamluks maximum morale.
7: Piety was at 95%, mostly through Piety events.
I played eu4 and hearts of iron in total about 330 hours, and as a very good strategy Gamer, I know this is wrong