Well pretty much everyone is doing that except the Nexus line. Can't really blame them for following the market.
Of course you can

It's not a deal breaker, everyone reading these forums has the potential to know not to use a charger that isn't designed for QC 3.0 with those phones and so can safely mitigate and enjoy the device - but for the general public it sucks, because they don't even know there is an issue to be mindful of, let alone the solutions. They definitely aren't aware that merely using the wrong charger can destroy their phone and/or start fires. The OEMs should have been smarter about this and followed the USB C and USB 3.0 or 3.1 specs accordingly. You can still get fast charging by following the specs, just not by using the Qualcomm method.