Strange, for a long time I've considered In the Wee Small Hours as "heavy" and Only the Lonely as self-parody. Well, hey, to each his own.
I basically agree with you, though I'd hesitate to call it "self parody." Perhaps you just prefer the film noir iconography of In the Wee Small Hours's cover art to the Pagliacci on velvet of Only the Lonely. \
Seriously, Sinatra mattered, but Sinatra impersonators are a blight. Learn from the man but don't ape him. He was a great artist, and like many of that breed something of a monster. Many of his fans love him precisely for his monstrous Las Vegas side, while many of his detractors can't get beyond that image. I'd advise both camps to simply listen to the music.
Nelson Riddle, of course, was a vital part of Sinatra's achievements. Neither man was as great without the other.