Of course the number of dimensions within a table-chart will have a big impact on the performance. If you used quite atomic dimensions within the charts which might have millions of rows and you apply 10 - 15 dimensions and some expressions you will create an object which needs to calculate billions of cell-values and plot them on the screen - even if your resources could handle this case it will be quite slow and also the usability will be rather poor. Therefore try to reduce the number of dimensions and rows.
If your table displayed the values correctly is depending on the quality of your used data and if you used a properly built datamodel.
In general each expression will be calculated and displayed for each dimension-value and you couldn't group or hide or caluclate them quite independently like in excel - you will always need a proper logic based on the used datamodel and on the object which is used to display the data. But this doesn't meant that you couldn't create flexible and performant views - there are a lot of possibilities, for example using several objects in containers, grid-views, visibility-conditions on dimensions and expressions, calculation-conditions and some more. Take for example a look here: