Dear,
I understand your question. Although I don't have the answer for it, and generally would agree with answer above (anything over it), I'm doing some tests on this field.
Nothing 'scientifically', but I'm playing with coating layers on some parts of my own car, even applying Wheel and Glass coating to portions of paint.
Away from that, I'm coating some test parts with layers of paint coating first, followed by Glass coating (which states to improve chip resistance), or wheel coating followed by Glass coating, etc.
Will I benefit from this? Maybe I would never be able to know for sure, but I'm doing observations on structure behavior (mainly water sheeting, beading, and easiness of cleaning), and I feel there may be some specific uses for this layering.
I plentiful encourage you to test a spot (why not do it in your front bumper), then you can observe how (if) different it behaves from the rest.
I even can't compare beading with Exo I've never used, but I can say PBL coating I've seen is insane, even my DD coated since november still beads like the day I applied the coating. I also do a lot of maintenance washes on PBL coated vehicles I've worked on, and coating properties in action always impress me.
The only con I'm seeing on my coating is that it feels 'dirty' after 'all this time', so I can't wait to have some time to rejuvenate it. My approach will be wash / clay and PBL Cleansing polish over it for a thorough cleansing.
See, the part tests I've told you I'm doing above (which may look useless), guided me through this approach.
I've noticed that PBL cleansing polish cleans very well and fully rejuvenates the coating.
Hope I've helped,
Sorry if sound confuse, but I've tried to share many ideas simultaneously so you can get a better view from my point. Ask if you need some clearance.
Kind Regards.