Shallow wasn't
And I swear I heard it in an interview with the band about a year before I'd even heard of PT. But I get what you're saying.
I actually heard Shallow quite a lot when Deadwing came out on one of my local stations, but I haven't heard it since (at least not within the last year, although defensively, I haven't listened to the radio much in between then either since I decked out my car's sound system). Notably though, the bridge was nearly cut out, with a few other radio edits that I forget, and it made the song considerably shorter, and definitely knocked down it's effectiveness.
Even still though, Shallow was about 4 and a half minutes long, and really a lot of radio singles are trying to be under the 3 and a half minute mark (ideally, radio stations try to keep it under 3 minutes long). Essentially what I'm trying to say, is that even though Porcupine Tree has made some "radio friendly" songs, they aren't really a band that can be considered "radio friendly," and be all around the airwaves at your local drug store. (It's not like you want to turn Steven Wilson into some teen pop idol though, right?)
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hey hey you you i dont like your porcupine tree