It is my understanding that Muslim’s are not guaranteed entrance to heaven by virtue of belief or works, I understand that even Mohammed is at the mercy of Allah’s will. I also understand that according to the Quran all people are born Muslim but not all people acknowledge this assumption. If this is correct I fail to see how Allah’s will could be considered to be fulfilled if all Muslims don’t go to heaven.
In the case of the Christian God it is true that he does want any to perish as this verse says.
9 The Lord is not delaying the promise, as some consider slowness, but is being patient toward you, because he* does not want any to perish, but all to come to repentance. (2 Pe 3:9).
My understanding is this, as a parent my will for my child is good, unfortunately my child doesn’t always choice what is good. This is how I understand God dealing with his creations he allows us to make choices, good and bad.
To contrast that I understand that in Islam there is only the will of Allah, no choice outside his will for the world.
I hope this helps.