I knew someone would rise to the bait with "you cannot put them in the same sentence, grrr". Spokette, my point is that all rock and pop performers from Bill Haley and the Comets onwards have been "marketed".
As you rightly point out, many artists like Sinatra and Elvis did not write the vast majority of their own music (although Colonel Tom Parker cannily ensured that Elvis got songwriting credits, knowing that this would be a better financial investment and paving the way for the "vanity credits" of today). If we are going to judge artists' musical quality by whether or not they write their own songs, then the Stereophonics are supposedly better than Elvis and Sinatra. And if we are going to judge them by whether they play instruments rather than "just" singing, then you'd have to say Brother Beyond and Bros are better than Diana Ross, Nat King Cole, Kirsty MacColl and Dusty Springfield.
I'm not sure in what way they "sing about nothing". Their songs are about love, loss, regret, affairs, one-night stands, duplicitous partners, betrayal, city life and the general confusion of twentysomethingness - so that'll be like, those of, ohh, pretty much every pop group of the last 40 years, then.
The production question is by no means as cut-and-dried as you have made it sound. A lot of modern pop groups like Girls Aloud, Take That, etc. have that very "polished" sound which only an excellent producer can give, but I look at it in the same way as I do the excellent editor working with a talented novelist - they give the final professional sheen to something which is already good but maybe a bit raw. Obviously they are not perfect. Cheryl's voice is quite thin. Sarah's is husky and more suited to big rocky numbers. And so on. But somehow, they achieve a kind of pop alchemy.
I bet you any money their songs will still be being played on the radio and in clubs and and parties in 20 years.