That's why Tatsu credits shouldn't be awarded for sitting in voice channels, but server points/score should since you can't spend those outside of the server. Also, the plan would be to allow the user to set which channels Tatsu does and doesn't award points to so that those in AFK channels would not be rewarded. If someone were to be idle in a channel that awarded points, Discord would naturally move them into the server's designated AFK channel, where points can't be awarded, which would effectively prevent farming.
However, if server owners were to allow farming, users would only be farming currency that could be spent in the server on server items, accolades, etc. If a server owner wants to allow farming, that would be up to them and the server's currency would lose value without affecting anyone not part of that server.
Thank you for the feedback though! Glad to know that some of the suggestions around here get noticed.