Super-human decision-making via pure elite rule
By having multiple people voting you can achieve higher reliability than any individual of the group. Instead of foolishly thinking than some individual human is super-great we can achieve greatness together.
Here the crux is that this super-human decision making requires the decisions by individual senators to be sufficiently independent from each other. There are multiple strategies to achieve that such as.
0. Letting each senator select a large number of advisors to help them make good decisions.
1. Have a diverse group of senators consisting of drastically different personalities, different sexes, etc.
2. separate the senators into several smaller groups.
3. not have any senator live close to another senator and not let more than 15% of them meet within the same nuclear blast radius.
4. Have status competition within the senate for higher executive positions (to the extent the senate event grants power like that).
A second benefit with 1 is that it allows more people to feel represented in the government due to there being more people like them there (here the feeling of representation is the only thing that actually matters, not the actual reality of the situation). It's important to maintain strong support for the ruling elite for the sake of a stable society.