Big fan of this, but powerpivot sits on vertipaq (I believe) which is an in memory columnar DB or sorts (apologies if that’s incorrect). So at this point you’re getting awfully close to direct querying (another msft feature) which while analogous resembles more traditional db/client if you squint hard enough.
But yes, big fan of vertipaq which I believe also powers PowerBI.
Just to clarify.. Yes, vertipaq is the tech behind power pivot, power bi and sql server analysis services (in tabular mode) and the same column-oriented storage is also used in sql server. Excel generates queries against the data stored in a vertipaq model. You cannot write normal excel formulas on top of it and you have to use DAX (a unique to msft language, which is the replacement for MDX) instead, which is pretty much a no-go for anyone but well-trained power users.
But yes, big fan of vertipaq which I believe also powers PowerBI.