Does it? That's the premise for creating this thread. How many attacks do you have to take before blur starts being better than mirror image?Blur definitely gets better for someone like a Bladesinger with Warcaster. Even with a 13 con and 16 int, my Bladesinger almost never loses concentration.
For example - say an enemy has a 50% chance to hit you. I'll even be generous and assume it never breaks your concentration.
Until the enemies have attacked you enough to kill all the mirror images on average then mirror image provides more protection than blur. They don't provide quite as much crit protection though - but still provide significant protection there as well.
The question is how fast will the mirror images go away? Not super quickly even in this scenario because they would have a high chance to be hit when targeted, but not 100%. They probably last you through 7-8 attacks on average.
In short - you might be overvaluing blur compared to mirror image in many circumstances.
It also cannot be removed by failing a concentration roll.Mirror Image, OTOH, relies less on anything other than the spell itself to protect you. Not something that is easy to quantify, but certainly a benefit.