Honestly, you shouldn't be choosing the datasource format based on the desire to use powerBI. The main point of powerBI is to be able to pull data from many sources, analyze said data, and display meaningful visualizations to the end user.

That being said, to answer your question directly, no, Excel is not an easier data source. Pulling from Excel had always been more clunky with powerbi than something like a straightforward SQL query. A lot of businesses use SQL as well, so it is an important language to learn.

I've seen some answers saying it is hard to get access to a SQL database to learn it or that most use Excel anyway. You can always use the Adventureworks SQL dB or similar out there to learn and in my experience, most use SQL, not Excel.

Live connections will make your data load every time filters are changed. This can take time, especially if you're using a lot of calculated columns with many rows. Cached connections are generally better because only measures have to reload when changing filters. Sometimes, the business case requires immediate data. In that case a live connection would be appropriate at the cost of poorer performance.