The goal isn't about guaranteeing that all states have X number of votes; the house and the senate vote separately on things. For a bill to pass the house and the senate requires:
1. A majority vote by the house whose members are allocated by population and therefore (ostensibly) represent the general population
2. A majority vote by the senate whose members are allocated by state and therefore (ostensibly) represent the will or needs of the states themselves.
As an example of why that distinction is relevant, consider Rhode Island. With a population of 1.1 million people, 100 reserved seats plus one seat per 500k would give Rhode Island 4 votes. Meanwhile, California's population of 38.9 million would give it 70 votes. That prohibits effectively representing Rhode Island as a state in any meaningful way.
As it is now, vote-by-population could allow a small number of states with the majority of population to out-vote the entire rest of the country, passing a law that states that all healthcare should be made free and the states have to pay for it themselves. Large states with strong economies and large tax bases might be in favor of that, but smaller and less populous states with weaker economies would go bankrupt.
Thus comes the senate, where a majority of states can decide that the law is inappropriate or against their interests and vote against it.
The distinction I think that most people from outside of the US probably don't fully understand is that, unlike in a lot of countries, each state is its own economy, government, politics, etc. rather than one sort of unified government that covers the whole country. Many of them see the federal government as not much more than a necessary evil to help the independent-but-united states coordinate themselves and prosper together. I remember someone once saying that it used to be "The United States are..." and not "The United States is..." and that kind of gives you an idea of the separation.
The best comparison might be the EU, where you could imagine the large, rich countries with large populations wanting to pass a vote that the smaller, poorer countries might chafe against. Imagine an EU resolution that said that all countries must spend at least 70 billion euro on defense; fine for large countries like Germany which already do, but absurd for a smaller country like Malta. The senate exists to prohibit that sort of unfairness in the US federal government.