But, as I pointed out, the Isaiah 65 passage is speaking literally of the new heavens and new earth. It seems to me you need to address that problem vis-à-vis dispensationalism before you can apply Isaiah 65 to your MK scenario.
I suspect our difference here lies in whether we equate Rev 21 new heaven and earth with the Isaiah 65 new heaven and earth.
Most dispensationalists see the Isaiah passage and the Rev passage as containing too many differences to equate them. Just the mere mention of infants excludes the Isaiah passage from being equated with the eternal state in Rev 21.