alot of this stuff is just simple differences of opinion.

The only thing I'd like to address is this idea that songwriting is worthless without good execution.

I've heard different versions of this same concept in this post and I think it's worth addressing. For me, I'm perfectly capable of saying 'that's a very well-written song but the production is horrible/the singing is horrible/the playing is horrible/etc.' Off the top of my head...a song like 'Heaven' by Bryan Adams comes to mind. Great composition but horrible execution....ripe for covering or re-interpreting.

Another way to illustrate this....haven't you ever heard a bad version of a standard like 'Summertime'? Hearing someone do shame to 'summertime' doesn't change the greatness of the composition right?
But what you're saying is that "all that would be moot if I didn't actually think the song was quality...if it was actually good or listenable." To me, the quality of the composition is not moot at all. You've simply heard a bad version of a well-written song.