Please just go play MK3 forever then, new games are for new content, a creatively stagnating series is a dead series and this is not a series that needs to die.
I think it's pretty safe that most of us fell in love with Mortal Kombat due to iconic characters such as Scorpion, Sub-Zero, Raiden, Mileena and many others. And many of those characters happen to be ninjas and other fancy archetypes, which had tons and tons of style and coolness to them.
No one in their right mind would say that someone like Cassie Cage or Jacqui Briggs have nearly as much style and coolness to them as your Scorpions and Mileenas.
I have nothing against new characters in franchises. I have nothing against new characters in Mortal Kombat. My favorites (Smoke, Noob Saibot and Rain) were also all new characters at one point. But they were all badass ninjas with cool looks and powers. Style and coolness overload. So they were destined to succeed, because that's what the majority of people likes. And that's also the reason why everyone always wants to see them in Mortal Kombat.
Cassie Cage, Takeda, Jacqui Briggs and Kung Jin however? Eh. Out of them all I personally like Takeda the most, because he is closest to what I've learned to love about Mortal Kombat. I couldn't care less about the others, because they're so basic.
And mind you that I'm mostly talking about the characters as "functions". I'm not saying that they have terrible personalities or are badly written characters or whatever. They do look bland compared to many other MK characters, but what really breaks it for me is that they lack anything special, which captivates my imagination. Smoke becomes sentient smoke. Noob Saibot shoots shadows. Rain traps you in water bubbles, shoots lightning and kicks you across the world. What does Cassie Cage do? She shoots her guns, kicks and copies her dad. What does Jacqui do? She shoots her rockets, punches and copies her dad. What does Kung Jin do? He shoots arrows and copies his cousin.
But at the same time what does D'Vorah do? She summons bugs, sprays venom, uses spikes hidden inside her body and much more. That's awesome. What does Takeda do? He uses deadly metal whips and teleports around. That's awesome. What does Erron Black do? He looks like a cowboy ninja and that's already more than enough. So new characters can be done right.
If Jacqui is in the game, then she needs to step up their game big time, otherwise people will continue complaining. And rightfully so. You calling them stupid won't make any of it less true.