I actually did do a
$ sudo dpkg -i epson-inkjet-printer-escpr2_etc_.deb
but it bombed out due to the unmet dependencies error, and then needed a
$ sudo apt --fix-broken install
to clean things up, which is why I then went down the $ sudo apt route.
The problem seems to be that the driver package is expecting lsb to be installed (since it is a dependency) and yet the instructions at Epson’s site, namely to do
$ sudo apt install lsb
are clearly no longer valid (whereas it may have been at some stage), since APT says there is no such thing to install.
So, the main question is: what is the workaround to get lsb installed on Byzantium/Bullseye in such a way that the printer driver package recognises that it is?