First some clarification. Power BI and Power Pivot both use Power Query as the foundation for data transformations. Your Power Query skills will transfer between the two (you'll notice that the PQ interface looks the same between the two because it
is the same).
Power Query
is M. By pressing the buttons in the UI, you are creating M. While you definitely don't need to be able to write M from scratch, by using Power Query enough you should get enough familiarity with the basics to be able to slightly tweak things as you need. Also, if you want to create any kind of custom columns in Power Query, you should know the basics, including roughly which functions are available to use. The main thing is probably to understand the
differences between the languages, and what they are used for.
It is possible to get by and build great dashboards without ever using DAX (that's how I started), but if you want to do anything more advanced as far as filtering or comparing values or more complex analysis, you'll want to use some of it eventually.
In another words, can I say by only learning these 3 (without learning the languages) that I I know these 3 well?
It really depends on whether or not you can answer the questions you want from your data, with only manipulating it in Power Query. If you can, then you're fine, but if not, you'll need to expand your skills further.
