In these sentences, tamyiz clarifies the respect in which one thing is greater or stronger.
أَنَا أَكْثَرُ مِنْكَ مَالًا
I have more wealth than you. مَالًا clarifies: more in what?
قُلْ نَارُ جَهَنَّمَ أَشَدُّ حَرًّا
Say: the Fire of Hell is more intense in heat. حَرًّا names the respect of intensity.
هُوَ أَفْصَحُ مِنِّي لِسَانًا
He is more eloquent in speech than I am. لِسَانًا specifies the respect of eloquence.