ESA and Universal Credit answer different questions
New Style ESA is mainly about contribution history and capability for work. Universal Credit is means tested and can include rent, children and other household support. That is why some people can be entitled to both, even though one can reduce the other.
If you only look at one system, you can misunderstand the overall position.
Why SSP often sits before both
If you are employed and off sick, SSP may be the first payment in the chain. Once SSP ends or is too low, ESA and Universal Credit become more relevant.
That is why the site architecture connects SSP, ESA and Universal Credit closely.
Use the right estimator for the right question
Use an ESA page to sense-check contribution-based support and pension interactions. Use Universal Credit pages when household income, rent and children are the bigger issue. The real-world answer is often not either-or.
This guide exists to make that split easier to understand.