polarity vs molecular size

Considering the boiling point of 1-iodohexane is 18x degree and that of 1-chlorohexane is 13x degree.

I want to know why the b.p. of 1-chlorohexane is lower as the polarity of chlorine is higher that means it is more polar than 1-iodohexane. Therefore, the van der Waal's force of 1- chlorohexane should be stronger and hence b.p. of it should be higher.

In my chem textbook, it states that "For molecules of comparable molecular sizes and shapes, van der Waal' forces depend ""largely"" on the polarity of molecules".

Also, for the polar molecules like 1-iodohexane, the molecules have already had permanent diople-permanent diople. Would dispersion force also exist?

*I am in dse level.