I don't know much about MRAP's but i've seen videos of turkish MRAP's blown into pieces with many dead soldiers. Some MRAP's were even unidentifiable after the blasts. Are these american MRAP's better?
To state this very clear in the beginning, I was in Iraq and Afghanistan in 2003 and 2005 respectively, but I was never in a MRAP. what I am about to say is my own opinion and people I know have been to one of these MRAP.
There are basically 3 sizes for MRAP, small, medium and large, all 3 have different uses and different level of protection.
Small MRAP (such as Caiman or Cougar 4x4) are designed for troop transport, it was to be used in low intensity conflict, its protection come from its thinner hull armor as well as it's chassis shape that were used to deflect the blast
Medium MRAP (such as Cougar 6x6) were used to provide Casevac , convoy duty, combat engineering and EOD vehicle. It's hull armor provide medium protection, used to medium to high risk area.
Large MRAP (such as Buffalo) is specialized Engineering Vehicle, they are designed to deal with maximum protection, and high risk area, if you are sending in one of these, that mean the road is mined or IED'ed for sure. These type of vehicle is used to Clear IED trap or mine in a known infected area.
MRAP is not god, however, it could withstand a 155mm artillery shell (which is about 41kg) projectile head on. (ie exploded underneath the MRAP)
But how do you detonate the shell also count, if you trigger the shell by rolling over it on its side, then the wheel and the axel would also take some blast damage and hence in basic theory, you can withstand a bigger blast.
The different between MRAP and IFV or Tank is, MRAP is driving like a truck, where you have a high driver seat angle, you can look at the road in front of you at about 4 to 5 ft distant. However, if you are in a tank or IFV (I used to be in a Bradley) even if you are turning out (meaning your torso seat outside the driver seat) at most you can see is 15 to 20 ft ahead of you, what happen on the road between your IFV and 20 ft ahead is basically hidden by the IFV own chassis. If you turn in, you can only see the road ahead a long way ahead of you (maybe 40 to 50 ft) as you are looking at the road in a periscope.
The most important defense for IED is situational awareness. If you see something wrong in the road ahead of you, then you know there are going to be an IED on that road hidden somewhere, so how much you can see out of in a MRAP, IFV and a Tank is actually more important than how much blast damage you can take in a tank or IFV, because the bigger the IED was, the easier you can spot them, but if you cannot look at the road ahead, then it doesn't matter if the IED is as big as a refrigerator, when you cannot see it, you are gonna get it.
This cougar is suspected had hit by a 500lb bomb IED
Hope this help