However they both started two dangerous precedent
6th - extramusical elements dictate the content of the Symphony. (I mean he repeated a motif 13 times with only slight variation in dynamics to represent nature. No self respecting believer in absolute music would do a thing like that and a development section that is simply transposing the same riff to different keys and far more harmonically stable then a new normal development section would entail. Haydn and Mozart would never have written such a basic development section even though it serves the calm extramusical narrative of the symphony)
9th - extramusical elements dictate the form of the Symphony with the ode to joy movement.
The fact that Beethoven still produced a brilliant work doesn't change that he started music decline after reaching it's peak with the 3rd and 5th Symphony