US Senator was an office initially designed to be selected by state legislatures rather than by direct popular election like the representatives. To a populist or a party boss, that might count as a spoiler to the will of the people or to the will of those in DC, or to both. But I may misinterpret GP's point.
I assume the person you're replying to is talking about the Filibuster and supermajority requirements not the direct election history. The filibuster is a senate rule not a constitutional design, so it wasn't part of the "design". Maybe they're both different ways of adding veto points to the same effect, but I think spoilers as "explicit design" is probably not how I'd describe it.
