A toddler mid-tantrum isn't manipulating you. Their prefrontal cortex, the part of the brain responsible for regulating emotion, is years away from being developed enough to do that job reliably.
What's happening in the moment
The emotional centers of the brain fire fast and hard, while the regulating structures are still under construction. A tantrum is, neurologically, a system running without its brakes yet installed. It isn't defiance.
What actually helps
Co-regulation, staying calm and present rather than trying to reason a toddler out of a meltdown, does more to build long-term self-regulation than any lecture delivered mid-tantrum ever could.