The US is a confederation, with the majority of the sovereignty resting with individual states rather than the Federal government, and
Senators are appointed by state legislatures and not directly elected, giving them a meaningfully different constituency and perspective than House reps.
Those circumstances existed when the Senate was initially conceived of by the founding fathers, but no longer do.
The Senate makes sense under two circumstances:
Those circumstances existed when the Senate was initially conceived of by the founding fathers, but no longer do.
How does that make the Senate important?