Fully agree, I have found that above 300k rows Excel struggles even on a good laptop. Not even mentioning the Python integration into MS Excel that is so unbearably slow that it is much better performing the calculations outside of Excel first.
These days I use DuckDB to read massive excel files. DuckDB now ships with a nice local UI and it also works beautifully with Datagrip, my preferred database IDE. With SQL, it just becomes a matter of applying old grease to do whatever analysis I want.
I am sold on the website looks and license model!