I don't expect max performance gaming on USB-C, but it should at least run as fast as it does on battery alone. It should definitely be able to update a mouse cursor and play an MP3.
This isn't just throttling, it's unusable. And it instantly goes away for a while when you disconnect and reconnect the USB-C power supply, even when gaming etc.
Oh, I fully admit that it could be tuned better. At least the 2023 G14 works reasonably well under linux this way, though I'm thinking of going through the ACPI and fixing some of that...