Lyrically, it's the difference between "The Cat in the Hat", and "Hamlet".
Baby Aspirin vs. Ultra-Strength Excedrin
Similac vs. Whole Milk
You are correct. We do a service once a quarter where we do only Wesley songs (with a beat and crunchy guitars), and I can tell you, that was one one annointed songwriter. I LOVE hymns, especially Wesley's.
But the place we're trying to take the congregation to is a lot more accessible if they aren't sitting there trying to figure out what a "Fount" is. Language changes. Styles change. Only God is constant.
After all, Wesley was quite "contemporary" in his day - and his songs were supplanting the traditional music of the time (which he found unaccesible to his generation, I might add). He faced a lot of opposition.