>such as that congress is likely to deadlock;
The bicameral requirement for a concurrent majority is entirely by design and has plenty of supporters. It's pretty egregious to cite this first on the list of supposedly crucial flaws.
>that its form of democracy is subject to unproportional divergence as state population sizes diverge, that by contrast adding new states is way too easy
The one fixes the other, but adding new states turns out not to be that easy. From a political standpoint, larger states have an outsize cultural and regulatory influence (which is known to the state of California to cause cancer, but which cannot be mentioned in textbooks used in Texas schools) so compensating smaller states makes sense; voters in large states who feel their votes are diluted should, in principle, be able to correct this with a split. Is it a perfect balance? Not at all, but it's something.
But in practice, adding new states has become too hard and this may be a source of recent political problems! Puerto Rico should have been a state in the '90s. Movements to split large states may not be such a bad idea.
>that elections at all are in no way shape or form necessarily fair
A cultural and political flaw, not a Constitutional flaw. Maybe an omission, but you can't write all of the laws and practices necessary for a fair election into the Constitution; it would take up most of the document!
>that the constitution isn't sufficiently amendable
A risk-averse and historically motivated bias; we had one bad Amendment (the 18th) and the fallout really put a damper on amendment movements.
>the lack of a checks on the presidency (clearly not intentional, but impeachment is a purely hypothetical check)
Trump's impeachment trial was heavily impacted by the Democrats' primary season and not-so-subtle party establishment hopes that Warren would somehow pull out a win, so everything had to be rushed in order to avoid distracting her (and she lost badly anyway).