List of artists that have never lost quality throughout entire career

Drag, a poor performance of Back has nothing to do with Bach himself.
Of course a rock.pop, country "artist" requires little to no talent or musical knowledge .

I’ve heard all the Brandenburg's played at least a hundred times live, never heard a bad performance yet . Neither has anyone else who goes to the best orchestras.

No one has ever said Bach was the greatest organist, all comments made in his life-time did said he was a master .
The most agreed upon  opinion among serious lovers of Classical Music worldwide is that he is the greatest composer who ever lived or ever will live .

Just saw this thread. In regards to new wave music only. I really like the old Depeche Mode but after Alan Wilder left they frankly have been making just childish crap.  DM's music has loss it's soul and the lyrics are simply childish.  With that said, the newly released 101 album on vinyl is fantastic. Some of the bands I think that have tested time are Radiohead, Blur, Tears for fears, U2, Johnny Marr and Echo and Bunnymen.  My taste in music is wide and vast.  Been listening to a lot jazz lately. Wish Coltrane and Monk were still alive. 

Of course a rock.pop, country "artist" requires little to no talent or musical knowledge .

Eddie Van Halen -- heavy metal, hard rock artist classically trained on acoustic guitar

Steve Vai -- jazz, jazz-rock, electronic rock multi-genre artist was classically trained on acoustic guitar.

Andy Summers -- jazz, rock, wave guitar artist former Police guitarist was classically trained by one of the greatest classical guitar maestro Emanuel Barrueco

Jan Akkerman -- classically trained on violin performs as lead guitar of jazz-rock band Focus

Jack Bruce -- classically trained on violin and performed as his most know act at Cream -- blues-rock power trio

Joey DiFrancesco -- jazz organist, jazz-rock -- self-trained since the age of 3 and performing since age of barely 7 at the stage (is there any talent?)

Irmin Schmidt -- electronic rock, kraut rock keyboardist and pianist -- alumni of Stockhousen Conservatory as pianist and orchestral conductor. Stockhousen Conservatory is school of innovative music and Jazz in Germany, but it also provides classical training. One of the most unusual schools of music in the world, but bare in mind that classical music rootes mainly from Germany and Austria and I believe still continue to add on...

There are many and many more rock or other ganre artists that literally infused J.S.Bach in their tunes and improvisations -- YES indeed he's one of the greatest, because his music still influences the most current tunes you hear -- just need to realize and just need to optimize judgments towards definitions of talent and musical knowledge. 

Country artists vary between family musical training and various schools of art. I may not find myself enjoying most of the country music, but I do find myself respectful to country artists skill to play instrument. When I hear Ricky Scaggs reefing acoustic guitar, I want to make it lowder, but when I hear his typical country style voice, I may want to shut it all the way down:-)

Classical music even nowdays still evolves, but not finding large enough listener due to commercial media. There are still classical composers of today finding their place mostly in the movie soundtracks. One of my favorite is Maurice Jarre.

I agree with @schubert , Bach was an one of a kind genius. His compositions are complex and beautiful. Anybody who plays the piano would tell you the same. 

czarivey. You seem totally unable to grasp  that in adult conversation some things are so obvious that the norm is to not  state them .
Of COURSE there are people in pop/rock, even country, that are talented and well educated as well.
However it is quite CLEAR that above is optional !