Well i dunno, it worked tremendously well for USB 2, don’t you think? Might be my age, but I distinctly remember having heaps of different charging cables. Gone, thanks to EU legislation.
You're not completely honest here, though. It was either Type A jack for power supplies without a cable, or Type B micro jack for fixed cables, and the latter very much specifies the port on the device.
Sort of. Standardizing on a USB-A charger did slightly push people to use a USB form plug on the other end - but data transfer is what really killed the proprietary connectors.
The multitude of USB connectors has been pared down - mini USB was withdrawn due to its design flaws, micro USB was obnoxious for 5Gbps data transfer, as was the larger USB-B plug. The convenience and capabilities of USB-C have slowly replaced them both on the device side, as well as the capability to go higher than 5 Gbps.
If anything has slowed adoption of USB-C, I'd point at desktop PCs and the reluctance to put 'real' USB-C ports on them. This is mostly because of what I consider to be a design error on the USB-IF's part - they added backward compatibility, allowing a USB-C dongle to supply a USB-A connector, when they should have supplied forward compatibility instead. This left a lot of bundled cables as well as hardware dongles like wireless mouse adapters stuck on USB-A.