That something is working as designed is not an endorsement if the design is bad.
The idea of compromise rarely survives the day. It's a 100% or zero game, lest we look like we actually agree with some of the other side... oh the horror.
Since value is subjective, there is literally no other viable definition of broken, and if you think this is a modern idea, you haven't seen much of history.
1) Things the founders got wrong on purpose. We've fixed a bunch of these, by e.g. broadening the franchise and ending chattel slavery with that whole Civil War thing. The way our Senate is composed is arguably an un-fixed one of these—it's that way on purpose, but it's, you know, bad.
2) Things they got wrong by accident. These are usually cases where politicking, application of game theory, and bad actors in general conspire to make things work differently than they were intended. This is stuff like the system stabilizing at two viable political parties, and the way the electoral college has worked in-practice almost from day one (but not the way the electoral college favors low-population states, because that part was on purpose, so would go under point 1 if we're regarding it as an error)
As originally designed, the US is not a nation with a strong central federal government that happens to be made up up 50 weak states and a handful of territories and districts. It's 50 strong states who happen to be united under one central but relatively weak federal government. In that context, having States represented equally, without regard to their populations, makes complete and total sense.
Completely by chance, that happens to indirectly overrepresent people you disagree with. That's unfortunate (depending on your ideology), but it certainly doesn't make the entire system broken or bad.
I would love to know what this by-definition version of "bad" is. That's a remarkable finding.
The Union is predicated on the States agreeing to certain terms and conditions that guarantee certain State Rights while compromising on others.
One such compromise is representation within the Union, whereby the Lower House (House of Representatives) has the States represented proportionally by population and the Upper House (Senate) has the States represented equally regardless their population. Territories that aren't a State receive no representation.
Additionally, the Lower and Upper Houses each have different duties and powers afforded to them. The Lower House legislates matters concerning money, among other things, while the Upper House legislates matters concerning government appointments and foreign diplomacy (eg: treaties), among other things. Both Houses must also agree with each other on any bills that are intended to go to the President for signing into law.
The States in the Union are tantamount to independent countries in most other contexts, so States' Rights are a very big deal.
Prior to 1913 Senators weren't even elected by the popular vote, they were elected by state legislators. Literally elected by the State. One could argue that actually makes more sense.