I think it's possible to become extremely proficient in Power BI in a very short time, but ONLY if you concentrate on the right things. Here are my Power BI "Super Six" areas in which to focus your efforts for the highest payoff:
Everything in PowerBI is optimized for star schema. If you build your analysis and reporting on the foundation of a solid data model, everything else will fall into place smoothly. Build on a broken data model and you're pretty much sunk right out of the starting gate...