Silly Rae, she should still be just a good making mix albums no matter what the physical media format is, though admittedly there's a lot less call for such in the age of digital distribution. Still, me thinks perhaps her real problem was a lack of confidence.
I wonder what use this talent makes her as general. Though for that matter, I don't think we know exactly what Triste and Makel's cutie marks mean.
She only says cassettes where replaced by those "circle shaped little bastards". MLP has always been a bit schizo tech, so maybe somehow tapes came first and were later supplanted by records, or perhaps those things are actually somehow CDs, or neither but rather just a completely different magitech that just looks like records.
...or most likely of all this blog, like most, happens in it's own separate AU with distinctive tech levels not indicative of the show.