You may not know who Tim Eilers is as he is an unsigned artist. He used to specialise in Numan covers and his mash-ups in particular are stunning. The thing is that he doesn’t pick two similar songs to mash up and that’s where his genius lies. Seriously talented guy.
Tim arranges, produces, plays, sings, records, and produces and stars in the videos. The end product is worthy of a major label release but it’s just a guy on YouTube who by day is a Hollywood VFX artist (he worked on Spider Man 3 and Black Adam)
He won't get anywhere doing copies. The hard part is creating original work.