How it can mange huge data, while it takes 3-4 hrs to merge max 55 MB data from excel files

This is a feedback for new Microsoft product Power BI which is making our life hell.

Lots of issues not tested and also taking time to address.

Now days merging of just 55 MB data is making my life hell and taking a long time almost 20 mins on every merge when I am trying to refer queries from the different query, while I am creating source within the same query it's throwing below error

Formula.Firewall: Query 'fx_SEE_U_CombinedData' (step 'FX_SEE_U_CombinedData') references other queries or steps, so it may not directly access a data source. Please rebuild this data combination.

My suggestion for Microsoft is, do not release any product before proper testing. All the source file is in MS Excel.

Not finding any way around and it's converting my nights in office hrs