I watched Final Space and I honestly don't agree these two are Hate Sinks.
Invictus' character is way too flat and alien to be particularly hateable. He is an Eldritch Abomination who is thousands of years old. Invictus has a manipulative personality and tries to turn Ash Graven against her friends by tricking her into thinking that Gary has killed her brother but other than that, he is not particularly hateable. He is your typical Eldritch Abomination Omnicidal Maniac who wants to escape from his prison and destroy the entire universe... for some reason.
The main reason why so many fans of the show started to hate him is simply because season 4 got cancelled which means Invictus is now a Karma Houdini. However, this doesn't make him a Hate Sink in any way.
The Lord Commander has too many Evil Is Cool moments and moments where he is played for laughs to count.
There is a moment where the LC tries to set a trap for the heroes and when they appear, he shouts "Surprise!". And then Gary says with a calm voice "Dude, no one is surprised" and that everyone expected this to be a trap. This enranges the LC and he complains h=that he spent many hours preparing the surprise and he even had the population of an entire prison slaughtered and it was all for nothing.
There is another scene at the very beginning where he interrogates a prisoner and the prisoner constantly interrupts him bu laughing at his height.
There is another scene where Little Cato, he is imprisoned by him, mocks him by saying that he looks like crap and that he always looks like crap but now he looks like the crap has decided to make a house of crap. This happens while the LC screams at him the shut up.
There is also a moment where the LC gives a speech to his followers and then he doesn't know how to turn the device off and there is an awkward moment where he doesn't know what to do while the soldiers are watching him and then he decided that he would just walk away.
There are a lot of other comedic moments I am currently fogetting but you get the point.
He is still played seriously enough to be Pure Evil, but I feel that his comedic moments still detract from the viewers' ability to hate him.
However, the main reason why I don't think he belongs to this trope is because he has too many Evil Is Cool moments especially after he becomes a titan. He single-handedly obliterates an entire planet with his new powers, he defeats several titans in battle that Invictus sends after him and he even attempts to take down Invictus himself and usurp him. I feel that he has too many cool moments and combined with some of his comedic moments, I don't think he should be listed as a Hate Sink.
This is just my opinion of course but while I watched the series, I never found them particularly hateable and I never got the impression that the creators were going out of their way to make the audience hate these characters.