The senate is inherently anti-majoritarian, in that it half of all senators can represent vastly more than half of all citizens. When you pile on a legislative super-majority it just becomes absurd. At a 60 vote requirement, something like 25% of the population potentially holds veto power over the other 75%.
That ain't mild.
The senate is fundamentally an anti-democratic rule-by-minority institution that represents land area over top of human beings.
Its as serious as a problem some other democracies and polities have faced
https://en.wikipedia.org/wiki/Rotten_and_pocket_boroughs
In the UK it almost caused a revolution, because it allowed the wealthy and corrupt to hold onto power, while denying representation to new cities with huge population.
https://en.wikipedia.org/wiki/Sejm_of_the_Polish%E2%80%93Lit...
https://en.wikipedia.org/wiki/Liberum_veto
In the Polish Lithuanian commonwealth every senator held veto power, in practice this meant that an insane amount of corruption occurred (including senators being bought off by foreign nations), and it totally neutered their power as a state to fend of military rivals, and eventually ended up with the nation conquered.
The senate is in desperate need of reform, and is a key part of why democracy is failing in the USA.