Most of the issues in this thread are related to poor hardware design more than a crowded spectrum. While the spectrum is in fact crowded in metropolitan areas, most Bluetooth communication doesn't require much bandwidth and can handle error prone areas with ease.
While the frequency hopping helps a ton on BL (and WiFi for that matter), the issues people outlined are due to:
1) Shitty firmware 2) Shitty hardware
Antenna design is black magic and only a few firms in the US do it well. It took us almost 10 months to fully design and test our antenna assembly(s) with a very capable third party firm.
It took dozens of trips to a test chamber, a dozen computer simulations that take a day to run, and PCB samples that take days to verify. They have to be tuned every time copper or mechanical parts move as well.
It's a real pain and most Bluetooth products use garbage chip antennas and baluns or reference designs for antennas. This increases the sensitivity to failure and provides a generally shitty experience.
Most of your product interactions around bluetooth are budget products connected on one side of the equation (e.g. a $50 bluetooth headset). So despite how capable your Mac or iPhone is, if you have a garbage headset on the other side with poor antenna design, it'll be a disaster of an experience.