Can I charge my iPhone 6 with an overpowered (2.4A) cable and powerbank?

I understand that the iPhone will not receive more than a certain amount of amps regardless of how powerful the cable or charger is. But if I use a 2.4A powerbank and a 2.4A 3rd party lightning cable, do I have reason to believe that my iPhone will somehow deteriorate faster because of the stronger power? Will the mechanism that regulates the power coming into the phone undergo more unnecessary stress because my accessories are 2.4a?

You may be able to but I wouldn't trust it

A faster charge will wear out your phone's battery faster but the wear rates are consistent with the expected lifespan of the device. Some modern non-flagship phones (supposedly) even limit the fastest possible charge rate in order to preserve the battery until the warranty period expires.

Generally speaking, your phone will not draw in more current than it negotiates with the charger no matter how much amperage is available in the power bank. There will logically be a strain on the chip that negotiates the charge rage (battery firmware?) but the device is built to accept (likely) tens of thousands of charges so the wear per use is negligible enough to ignore. However, it's generally wise to only use the power bank for emergency recharge purposes. Minimize its use regardless. To maximize the power bank life, keep it charged around 30-80% of the maximum and avoid storing in high heat conditions (unless its for emergencies in your car. Then its best to leave it in there).

the simple fact that you don't hear other people voicing this same complaint probably tells you that there are no credible concerns associated with what you want to do.

It makes absolutely no different how high current rating the external source is, as long as it's 5V with a USB connector.

The phone will charge at whatever limit the designers chose to be suitable for it's battery. Nothing will over-ride that to increase it in any way.

It will not cause any/faster degradation of the electronics or battery.

The only thing to be wary of, no matter what charger you use, is to make sure the phone has good airflow around it while charging - try and avoid charging with laid flat on any surface (prop it up on something) and never on a soft surface that traps heat.

Heat is the big killer for lithium batteries, especially when near full charge.

[Electronics designer & programmer for 40+ years].