It is really hard to say whether or not the internet is a threat to musicians.  For right now, it is a definite asset because if you are really talented, you can put your stuff anywhere and everywhere for everyone to see.  If you have the resources to keep creating and creating and you are just different enough to be intriguing and fresh, your name and materials will slowly begin to spread.  Once they do begin to spread, you have to keep creating still, because the public will forget about you just as quickly as they started to like you.  I can also understand how anyone being able to put whatever they want online might hinder talented artists because if everyone is doing it, it raises the competition level a lot higher.  There is so much different music and videos uploaded every day, it makes everything so diluted.  One really has to catch the attention of a lot of people.  The money making side is a whole different thing.  The internet has opened a lot of new ways for artist to make money off of their works, but it has just as much created a way for them to lose it as well.  If one is careful, they can do a good job of making sure their music cannot be downloaded for free from any source, but that is probably not an easy thing to do when all you are trying to do is get your name and work out there.  That is what seems to be the best way to do it now though.  The best way to become successful through music on the internet is to put a whole bunch of your stuff out there for free at the beginning.  Then when a lot of people like what you do, that is when you make new material and make it only available for purchase.  That is what Tyler the Creator did and that is what Donald Glover/Childish Gambino did, and they are both very successful.