My sense is that renaissance listeners just wouldn't really know what to do with contemporary music. It's quite a different soundscape, and you might as well ask what they would have thought about Balinese Gamelan music. Any kind of communicative system requires a significant period of immersion to gain familiarity with what's going on in it, else it all just sounds like gibberish. In language, this is what is meant by the phrase "its all Greek to me." Obviously, Greek is a sophisticated linguistic system that, for people fluent in it, can be used to communicate basically whatever you want. But, for an outsider, any random string of Greek words sounds just as good as any other random string. So whether you're reciting the Odyssey or gobbledygook, "it's all Greek to me."

So I really don't think that comparing Renaissance tastes directly to modern ones is that productive. Especially because the notion of what music was designed to do, why someone would listen to music, and what it means for something to be good have changed do much. For instance, the only things we really have access to to judge what was thought of as "good" music in the Renaissance are A) church doctrine about music and B) critical writings about music in theory treatises.

The former is way less enlightening than you'd think. Religious doctrine didn't really care too much about the details of musical practice too much (for instance, the supposed ban on the tritone as the "devils interval" in catholic music is likely complete fiction), all they really cared about was general things like "keep shit simple" or "don't let the music distract one from the words." Theory treatises are way more detailed, but sometimes it's hard to tell how much of what they're saying captures the cultural Zeitgeist of the day and how much of it is grumpy musings of someone with very particular tastes who happens to have access to a printer. Like, a guy named Johannes Tintoris is a hugely important theorist of the late 15th century who has a lot to say about what's bad in music. But many of the things he says are bad in music (like certain ways of handling tritones) you can find all over the works of the most popular composers of his day, including people who had key positions such as at Sistine Chapel.

So in short, it's really hard to say what people actually thought was good or bad about music at this time. Things like song structure (for instance, the various "fixed forms" such as the rondeaux and the viralei) were not "good" or "bad" things about music, they just simply were. The same is true of "grammatical" things like how counterpoint worked. Modern pop music uses a quite different approach to counterpoint and structure, it's true, but I don't think it'd be heard as "bad." More like "wait, what the hell even is this?" I think it'd be pretty easy to recognize that this shit isn't even operating with the same grammar. The question is whether they'd be open to learning a new grammar or not.

So rather than asking "how would Renaissance musicians think about today's music," I think a more productive way into this issue would be to just forget about comparisons and just dive into what people did compositionally in the time period, and then comte back to pop music with new perspective. In that sense, you should look into books on Renaissance counterpoint, such as the one authored by Peter Schubert.

It wasn't specifically about Renaissance music vs modern pop, but I did talk about some of the musical differences between Beethoven and 'Roll Over Beethoven' here - hope that helps! The main thing I'd add to that is that Renaissance music - Tallis, Palestrina, etc - is often sacred music with religious meaning suffused through it; there would likely be Renaissance listeners offended at the secular nature of much modern pop music, perhaps for similar reasons to how religious fundamentalists today are offended at the modern pop music's secular nature (though there also were people writing more secular music at the time - most notably Robert Johnson who likely wrote much of the music in Shakespeare's plays, which is obviously secular).