You'd have to check carefully the terms of the Chase coverage, but I expect that they require you to reject all optional coverage for loss or damage to the rental vehicle in order for the Chase coverage to apply.

If you plan to continue to rent cars costing more than $75K, you might be better off enrolling one of your Amex cards -- even ones with no annual fee -- in Amex's Premium Car Rental Protection program. For $24.95 per rental (less for California and Florida residents), you are covered for up to $100,000.