Doesn’t it have some weird and Very Apple design flaw where it’s hard to charge and use at the same time?
That's not "their old mouse", it's the current mouse. We're still on the 2015 design with the charging port at the bottom. (I have one and I don't mind/care, I just chuckle once a month when I remember to charge it)
The annoying Apple limitation is that you can't hot-swap the battery.
I am sure USB-C with PD will be available at some point, but it's not a majority of economy today AFAIK