Part of what helps make each form of Zeztz work as well as it does is that it acts as an extension of the base forms.
You can see with the Physicam forms and the Technolom forms. Each ability acts as an extension of the idea they're based on, but I do admit I wish Esprim and Paradigm had a third Capsems just to even things out with other base forms.
Maybe Esprim's third Capsems could grant Zeztz the ability to generate plant growth, and Paradigm's third Capsems could make Zeztz invisible. Zeztz's theme is being a spy so it would be fitting.
What's also helpful is that each form truly feels earned.
Each power expands Baku's character growth, like with Plasma, where, despite being warned about the true nature of Capsems by Nox, Baku ultimately confronts the mysteries and nightmares of his past and thus gains a new power, and Catastrom, which was gained from Baku's desire to kill Nox after he cause the of the other agents and cause more choas in the world.
And while the world did reset, Baku is still haunted by trauma from those events, which leads to the people wanting to prevent that dark future.