Need Advise On SharePoint to Datamart or Dataflow

So i need advise where like there is a situation my source data is from SharePoint site and previously by building report i connected with shraepoint only the data gets added monthly now when in a particular month the data became so large that it couldnt fit in a single excel sheet so they made or splitted it and while adding new data the schema also changed inconsitent columns and header names and son on now the data some of the data is missing like some month and now they are saying that the data will become exponentialy larger so the previous etl in power query which had done is also slowing and refresh is also taking very much time so i was thinking to you know get the data from sharepoint using dataflow and dump it in a datamart for better performance and scalability ....... will it be a good solution anything would help or any alternate methods as a fresher just into this itindustry and this tool i dont have that much idea by reading the microsoft forum and learn material i came to this idea ...... any better methods or is this viable solution would help 

Thanks in Advance