Yup, you got it. Sorry about the broken docs formatting, we're fixing that. In the meantime you can click through to the source code (click the class name at the top of the doc page) and read the doc comments in there.
Both solutions massively violate my coding conduct
When I ran into this yesterday, I decided to rewrite my CSS and go with the standard markup instead. Everything else gave me the willies.
Haven't even looked as far as how to use a custom BoundList implementation in ComboBox. There should really be an easy way to override the implementing class when using composition. Duplicating the createPicker code could easily be avoided if the code delegated instantiation to a factory method , or - facilitating the Ext4 class loading pattern - just allow configuration of the class name as a config property.
Admittingly, reconfiguring the tpl in BoundList after callParent wouldn't be THAT bad - just not very nice since we execute code and then throw away the result.