lol wow, so much praise for Apple's way of implementing things.
As for Fast Charge, I thought you enabled it on both your Galaxies because you didn't care about the deterioration, or thought it would be minimal over time?
I get the confusion around USB-C since it was supposed to be the standard but turns out it has no standard.
But is that really an issue if you buy first party cables from OEMs? Like a Samsung or Apple USB-C cable? Or even a reputable third party, like Anker or Monoprice?
There were faulty Apple, Anker and Monoprice cables (who thinks Monoprice is reputable?).
Most were recalled, but you're not guaranteed to get a good cable because you bought it from Anker.
Samsung's USB-C cables are completely not up to spec and are build to support Fast Charge (which is against USB 3 spec and violates USB-C spec), but they are safe for power delivery as well and are safe to use.
Also, each of the "good" cables that won't burn your house down has its own specs and protocols that it supports. You can buy a $50 cable from Apple, but it won't support Thunderbolt or Quick charge. Some that they sell are still USB 2.0 entirely, and only a Thunderbolt Type-C cable actually supports Thunderbolt, but it's not up to USB 3.1 spec.
Buy one from Sony and it will do Quick Charge but won't support anything other than 3.0 data transfer and Quick Charge. Then Quick Charge in the first place is in violation of USB 3 and Type-C spec as well by the way, as USB-C spec calls for Power Delivery being the only allowed fast charging method on USB-C. Thunderbolt 3 is in spec, but almost no cables support it etc.
I use exclusively Wireless charging on my phones, or whatever I can.
The Fast Charge deterioration is not exactly minimal, and it's more pronounced the faster the fast charging is. For instance, Samsung is very conservative with the amount of power they allow their phones to push - Since the Note 7 drama, the S8, S9 and S10 also ensure that the battery remains fairly cool during charging even at the expense of not delivering full 10W to their phones to mitigate damage to the battery from fast charging. Other OEMs these days go balls to the wall with pumping juice into their batteries, which is horrible really, but people seem to make "whoever charges faster" a competition now, not caring that their phones have trash battery life after a year.
The general rule is that after a certain "sweet-spot" level, the faster your battery charges, the more it degrades.
If you go with something like Samsung's current Fast Charge, that's fairly safe and degradation should be minimal due to it being overengineered for safety and also not being THAT fast.