They put immortal on Barbarian because they gave the Immortal an AC calculated by 8+dex+Con, which they realized was the Barbarian. The Immortal is all about defense, healing, and being really hard to kill. Kind of like the Barbarian.
The psychic warrior is a warrior. A Fighter. Focusing on attack and is basically an Eldridge Knight with Psionics instead of magic.
The Soul Knife is a dexterous skirmishes who has such control over their mind’s powers, they can create a blade from pure mental strength. Like a psychic ninja. So it’s a Monk class.
The Lurk is going to be a sneaky type who slips in and out of peoples minds like a thief in the night. Thus, a Rogue class.
The keneticist or whatever they decide to call it is a blaster wielding the forces of nature to blow things up. We already have one of those. It’s called a wizard. Why create a new system of throwing fireballs when you can just give wizards access to psionic powers and be done with it? Thus, a wizard class.
It’s not “too many subclasses”. It’s just that there are a lot of psionic archetypes, too many for a class to do justice. That is what was wrong with the Mystic. It could be anything. Well, now many classes can have a little psychic flavor, utilizing the chassis of that class to give the variety. Why make the Psion able to use weapons and/or armor, or force all Psion to have a higher hit dice, when the fighter gives everything you need and the subclass can give the Psionics?
The Psion class itself will be the person who only focused on Psionics, and therefore has his own flavor. I like this take. It allows the Psion to be its own thing, while still allowing those archetypes that players like, such as the fighting psychic, the ninja psychic, the sneaky psychic, and the wizard who delved into psychic powers.