Have to agree with others, that the spell selection thing is probably due to an engine limitation. I also agree that I would not have chosen Vicious Mockery. There is also the casting stat issue. It may well be necessary to create warlock-specific versions of a spells in order for it to use Charisma instead of Wisdom (Thorn Whip).
Which brings us to Shillelagh, which has a big overlap with Pact of the Blade.
Which brings us to the pact-specific invocations if they are in the game. Blade should need Thirsting Blade to get it's second attack, and Book should need Book of Ancient Secrets to cast ritual spells. But BG3 does not have ritual spells. My guess is this will be replaced by three spells that would be rituals in PnP that you can cast once per long rest. Something like Find Familiar, Detect Thoughts and Speak with Animals.
