Because dull and callous are essentially synonymous, I do not see why you can say one is more exactly the "lexical definition" than the other.
IOW, couldn't/shouldn't you also have referred to "dullness on the blade"? (logically speaking :^)
I say what I did because I read the Lexicons. Also, because I think consistency is good in translation and theology. Also, because many of such tools are more contemporary than old English, which I don't use:
NKJ Matthew 13:15 For the hearts of this people have grown dull. Their ears are hard of hearing, And their eyes they have closed, Lest they should see with their eyes and hear with their ears, Lest they should understand with their hearts and turn, So that I should heal them.'
NET Matthew 13:15 For the heart of this people has become dull; they are hard of hearing, and they have shut their eyes, so that they would not see with their eyes and hear with their ears and understand with their hearts and turn, and I would heal them.'
ESV Matthew 13:15 For this people's heart has grown dull, and with their ears they can barely hear, and their eyes they have closed, lest they should see with their eyes and hear with their ears and understand with their heart and turn, and I would heal them.'
NAS Matthew 13:15 For the heart of this people has become dull, And with their ears they scarcely hear, And they have closed their eyes Lest they should see with their eyes, And hear with their ears, And understand with their heart and return, And I should heal them.'
KJG Matthew 13:15 For this people's heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed; lest at any time they should see with their eyes, and hear with their ears, and should understand with their heart, and should be converted, and I should heal them.
KJV Matthew 13:15 For this people's heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed; lest at any time they should see with their eyes, and hear with their ears, and should understand with their heart, and should be converted, and I should heal them.
NIV Matthew 13:15 For this people's heart has become calloused; they hardly hear with their ears, and they have closed their eyes. Otherwise they might see with their eyes, hear with their ears, understand with their hearts and turn, and I would heal them.'
Please feel free to add your own elaboration. When I showed the Greek and the Hebrew showing dull comparing to insensitive, I thought that would suffice. If you like dull vs. sharp, then I'll let you explain how sharp means sensitive.